Fair Value Measurement - Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Financial assets:
Loans held for sale	$ 347	$ 191
Level 1
Financial assets:
Cash and cash equivalents	4,903	5,193
Restricted cash for securitization investors	458	400
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	38,394	25,663
Restricted cash for securitization investors	0	0
Net loans held for investment	0	0
Loans held for sale	515	11
Interest receivable	2,478	2,104
Other investments	1,329	1,326
Financial liabilities:
Deposits with defined maturities	82,990	45,531
Securitized debt obligations	18,067	16,918
Senior and subordinated notes	31,524	30,744
Federal funds purchased and securities loaned or sold under agreements to repurchase	538	883
Interest payable	649	527
Level 3
Financial assets:
Cash and cash equivalents	0	0
Restricted cash for securitization investors	0	0
Net loans held for investment	308,044	302,920
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	43,297	30,856
Restricted cash for securitization investors	458	400
Net loans held for investment	305,176	299,091
Loans held for sale	507	11
Interest receivable	2,478	2,104
Other investments	1,329	1,326
Financial liabilities:
Deposits with defined maturities	83,014	45,858
Securitized debt obligations	18,043	16,973
Senior and subordinated notes	31,248	30,826
Federal funds purchased and securities loaned or sold under agreements to repurchase	538	883
Interest payable	649	527
Estimated Fair Value
Financial assets:
Cash and cash equivalents	43,297	30,856
Restricted cash for securitization investors	458	400
Net loans held for investment	308,044	302,920
Loans held for sale	515	11
Interest receivable	2,478	2,104
Other investments	1,329	1,326
Financial liabilities:
Deposits with defined maturities	82,990	45,531
Securitized debt obligations	18,067	16,918
Senior and subordinated notes	31,524	30,744
Federal funds purchased and securities loaned or sold under agreements to repurchase	538	883
Interest payable	$ 649	$ 527