Fair Value Measurement - Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Financial assets:
Loans held for sale	$ 394	$ 347
Level 1
Financial assets:
Cash and cash equivalents	5,298	4,903
Restricted cash for securitization investors	2,415	458
Net loans held for investment	0	0
Loans held for sale	0	0
Interest receivable	0	0
Other investments	0	0
Financial liabilities:
Deposits with defined maturities	0	0
Securitized debt obligations	0	0
Senior and subordinated notes	0	0
Federal funds purchased and securities loaned or sold under agreements to repurchase	0	0
Interest payable	0	0
Level 2
Financial assets:
Cash and cash equivalents	40,116	38,394
Restricted cash for securitization investors	0	0
Net loans held for investment	0	0
Loans held for sale	426	515
Interest receivable	2,494	2,478
Other investments	1,330	1,329
Financial liabilities:
Deposits with defined maturities	79,639	82,990
Securitized debt obligations	17,323	18,067
Senior and subordinated notes	30,705	31,524
Federal funds purchased and securities loaned or sold under agreements to repurchase	715	538
Interest payable	668	649
Level 3
Financial assets:
Cash and cash equivalents	0	0
Restricted cash for securitization investors	0	0
Net loans held for investment	306,948	308,044
Loans held for sale	0	0
Interest receivable	0	0
Other investments	0	0
Financial liabilities:
Deposits with defined maturities	0	0
Securitized debt obligations	0	0
Senior and subordinated notes	0	0
Federal funds purchased and securities loaned or sold under agreements to repurchase	0	0
Interest payable	0	0
Carrying Value
Financial assets:
Cash and cash equivalents	45,414	43,297
Restricted cash for securitization investors	2,415	458
Net loans held for investment	301,537	305,176
Loans held for sale	414	507
Interest receivable	2,494	2,478
Other investments	1,330	1,329
Financial liabilities:
Deposits with defined maturities	79,848	83,014
Securitized debt obligations	17,291	18,043
Senior and subordinated notes	29,925	31,248
Federal funds purchased and securities loaned or sold under agreements to repurchase	715	538
Interest payable	668	649
Estimated Fair Value
Financial assets:
Cash and cash equivalents	45,414	43,297
Restricted cash for securitization investors	2,415	458
Net loans held for investment	306,948	308,044
Loans held for sale	426	515
Interest receivable	2,494	2,478
Other investments	1,330	1,329
Financial liabilities:
Deposits with defined maturities	79,639	82,990
Securitized debt obligations	17,323	18,067
Senior and subordinated notes	30,705	31,524
Federal funds purchased and securities loaned or sold under agreements to repurchase	715	538
Interest payable	$ 668	$ 649