Fair Value Measurement - Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Financial assets:
Loans Held-for-sale, Fair Value Disclosure	$ 314	$ 191
Level 1
Financial assets:
Cash and cash equivalents	4,620	5,193
Restricted cash for securitization investors	435	400
Net loans held for investment	0	0
Loans Held-for-sale, Fair Value Disclosure	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	40,249	25,663
Restricted cash for securitization investors	0	0
Net loans held for investment	0	0
Loans Held-for-sale, Fair Value Disclosure	440	11
Interest receivable	2,469	2,104
Other investments	1,329	1,326
Financial liabilities:
Deposits with defined maturities	78,833	45,531
Securitized debt obligations	17,409	16,918
Senior and subordinated notes	31,051	30,744
Federal funds purchased and securities loaned or sold under agreements to repurchase	522	883
Interest payable	685	527
Level 3
Financial assets:
Cash and cash equivalents	0	0
Restricted cash for securitization investors	0	0
Net loans held for investment	305,810	302,920
Loans Held-for-sale, Fair Value Disclosure	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	44,869	30,856
Restricted cash for securitization investors	435	400
Net loans held for investment	299,825	299,091
Loans Held-for-sale, Fair Value Disclosure	428	11
Interest receivable	2,469	2,104
Other investments	1,329	1,326
Financial liabilities:
Deposits with defined maturities	79,176	45,858
Securitized debt obligations	17,417	16,973
Senior and subordinated notes	31,283	30,826
Federal funds purchased and securities loaned or sold under agreements to repurchase	522	883
Interest payable	685	527
Estimated Fair Value
Financial assets:
Cash and cash equivalents	44,869	30,856
Restricted cash for securitization investors	435	400
Net loans held for investment	305,810	302,920
Loans Held-for-sale, Fair Value Disclosure	440	11
Interest receivable	2,469	2,104
Other investments	1,329	1,326
Financial liabilities:
Deposits with defined maturities	78,833	45,531
Securitized debt obligations	17,409	16,918
Senior and subordinated notes	31,051	30,744
Federal funds purchased and securities loaned or sold under agreements to repurchase	522	883
Interest payable	$ 685	$ 527