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.

General ledger accounting is the financial backbone every other SAP module ultimately posts into, so FI interviews - and increasingly cross-module interviews since S/4HANA's Universal Journal unified everything - lean heavily on this topic to confirm a candidate understands double-entry bookkeeping as SAP implements it, not just transaction code navigation.

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

Every company code is assigned a chart of accounts (a list of G/L accounts usable across that company code, potentially shared across multiple company codes for group reporting consistency), and each G/L account carries both a chart-of-accounts-level segment (account group, account type) and a company-code-level segment (currency, tax category, whether it's reconciliation-relevant). Every financial document posted (FB50, or generated automatically from MM/SD postings) consists of at least two line items (debit and credit) following double-entry principles, tagged with a document type (e.g., SA for G/L posting, KR for vendor invoice) and posting keys (40/50 for G/L debit/credit, 01/31 for customer/vendor debit/credit) that determine account type and debit/credit direction.

FB50

A classic distinction interviewers probe is reconciliation accounts - special G/L accounts (like the main AR or AP control account) that cannot be posted to directly; they're updated automatically whenever a posting happens to a subsidiary ledger account (customer or vendor), keeping the G/L in sync with AR/AP sub-ledgers without allowing a direct out-of-band posting that would break reconciliation. In S/4HANA, the Universal Journal (table ACDOCA) merges what used to be separate FI, CO, AA (asset accounting), and material ledger tables into one single line-item table, eliminating the reconciliation gaps and separate totals tables (like the old GLT0) that plagued classic ECC reporting.

ACDOCAGLT0

A senior-level answer also covers parallel accounting via ledgers (leading ledger 0L for the primary accounting principle, non-leading ledgers for local GAAP/IFRS differences) and how document splitting (new G/L functionality) enables generating a fully balanced financial statement per profit center or segment even when the original posting wasn't naturally balanced at that granularity, which is essential for accurate segment reporting.