Financial Accounting (FI): General Ledger & Document Posting

Core FI concepts: chart of accounts, G/L accounts, document types, posting keys, and the universal journal in S/4HANA.

Every module eventually posts into FI. A goods receipt in MM, a billing document in SD, a payroll run — all of them end as accounting documents in the general ledger.

A reconciliation account is like an ATM's master balance sheet that updates itself automatically every time a customer's individual account moves, so the branch total is always correct without a teller ever posting directly to the master balance by hand - and the Universal Journal is like replacing four separate ledgers kept by four different departments with one shared ledger everyone writes into and reads from simultaneously.

Key Concepts

Double entry, enforced. Every document has at least two line items and they must balance:

    debit   inventory       10,000
    credit  GR/IR clearing  10,000

SAP will not post an unbalanced document. That constraint is the foundation everything else sits on.

Two attributes control each posting.Document type says what kind of document it is: SA for a general ledger posting, KR for a vendor invoice, DR for a customer invoice. It also controls the number range and which account types are allowed.

SAKRDR

Posting key says what each line does:

    40  G/L debit          50  G/L credit
    01  customer debit     15  customer credit
    21  vendor debit       31  vendor credit

So the posting key determines both the account type and the direction, which is why the same key means the same thing across every document.

The chart of accounts lists the G/L accounts a company code may use. Each account has a chart-of-accounts segment (account group, type) and a company-code segment (currency, tax category) — the same account can behave differently in different company codes.

Reconciliation accounts are a concept worth being precise about. The main receivables account cannot be posted to directly. It is updated automatically whenever anything is posted to a customer account.

That is the mechanism keeping the general ledger and the sub-ledger in step. If you could post to it directly, the ledger total and the sum of customer balances would diverge, and nothing would detect it.

The Universal Journal is the S/4HANA change. In ECC, FI, CO, asset accounting and the material ledger each had their own tables and their own totals, and reconciling them was a recurring task.

    ECC        BKPF/BSEG + COEP + ANEP + ... + totals tables (GLT0)
    S/4HANA    ACDOCA -- one line item table, no separate totals

One table, one version of each line, and the reconciliation problem largely disappears. Totals are computed on the fly, which is only practical because HANA can aggregate fast enough.

Two more for a senior answer.Parallel ledgers. The leading ledger 0L carries the main accounting principle; non-leading ledgers carry local GAAP or IFRS differences, so one posting can be valued differently for different reporting requirements.

Document splitting. A posting that balances at company code level may not balance per profit centre or segment. Splitting distributes the lines so a balanced balance sheet can be produced at that finer level — which is what makes segment reporting possible at all.

What the interviewer is probing.1. "What is the new general ledger's main advantage?" Probing: currency. Stalls: "It is newer." Moves up: document splitting, which gives balanced books by segment or profit centre without separate special ledgers.

2. "What makes a posting document complete?" Probing: the fundamentals. Stalls: "Entering amounts." Moves up: balanced debits and credits per currency, a valid posting period, and the required fields from the field status group.

3. "What is a reconciliation account?" Probing: the structure. Stalls: "A GL account." Moves up: the GL account a subledger posts to automatically, which is why you cannot post to it directly — it keeps AR and AP tied to the GL.

4. "Why would a posting period error appear?" Probing: troubleshooting. Stalls: "A date typo." Moves up: the period is not open for that account type in OB52, which is a deliberate control rather than a fault.