Fair Value Measurement - Schedule of Fair Value of Financial Instruments (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Financial assets:
Securities held to maturity	$ 26,196	$ 25,317
Level 1
Financial assets:
Cash and cash equivalents	4,185	8,023
Restricted cash for securitization investors	2,517	1,017
Securities held to maturity	199	198
Net loans held for investment	0	0
Loans held for sale	0	0
Interest receivable	0	0
Other investments	0	0
Financial liabilities:
Deposits	25,502	25,847
Securitized debt obligations	0	0
Senior and subordinated notes	0	0
Federal funds purchased and securities loaned or sold under agreements to repurchase	0	981
Other borrowings	0	0
Interest payable	0	0
Level 2
Financial assets:
Cash and cash equivalents	5,791	0
Restricted cash for securitization investors	0	0
Securities held to maturity	25,962	25,068
Net loans held for investment	0	0
Loans held for sale	1,038	860
Interest receivable	1,351	1,189
Other investments	2,020	2,060
Financial liabilities:
Deposits	211,580	15,848
Securitized debt obligations	18,920	16,225
Senior and subordinated notes	23,774	22,062
Federal funds purchased and securities loaned or sold under agreements to repurchase	992	0
Other borrowings	17,180	20,134
Interest payable	327	299
Level 3
Financial assets:
Cash and cash equivalents	0	0
Restricted cash for securitization investors	0	0
Securities held to maturity	35	51
Net loans held for investment	242,935	222,007
Loans held for sale	0	73
Interest receivable	0	0
Other investments	9	0
Financial liabilities:
Deposits	0	169,227
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
Other borrowings	0	0
Interest payable	0	0
Carrying Amount
Financial assets:
Cash and cash equivalents	9,976	8,023
Restricted cash for securitization investors	2,517	1,017
Securities held to maturity	25,712	24,619
Net loans held for investment	239,083	224,721
Loans held for sale	1,043	904
Interest receivable	1,351	1,189
Other investments	2,029	2,060
Financial liabilities:
Deposits	236,768	217,721
Securitized debt obligations	18,826	16,166
Senior and subordinated notes	23,431	21,837
Federal funds purchased and securities loaned or sold under agreements to repurchase	992	981
Other borrowings	17,211	20,131
Interest payable	327	299
Estimated Fair Value
Financial assets:
Cash and cash equivalents	9,976	8,023
Restricted cash for securitization investors	2,517	1,017
Securities held to maturity	26,196	25,317
Net loans held for investment	242,935	222,007
Loans held for sale	1,038	933
Interest receivable	1,351	1,189
Other investments	2,029	2,060
Financial liabilities:
Deposits	237,082	210,922
Securitized debt obligations	18,920	16,225
Senior and subordinated notes	23,774	22,062
Federal funds purchased and securities loaned or sold under agreements to repurchase	992	981
Other borrowings	17,180	20,134
Interest payable	$ 327	$ 299