Fair Value of Financial Instruments - Schedule of Fair Value of Financial Instruments (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Financial assets:
Securities available for sale	$ 39,665	$ 41,800
Securities held to maturity	22,928	19,185
Derivative assets	836	959
Financial liabilities:
Derivative liabilities	369	710
Level 1
Financial assets:
Cash and cash equivalents	6,148	6,291
Restricted cash for securitization investors	405	874
Securities available for sale	4,373	960
Securities held to maturity	0	0
Net loans held for investment	0	0
Loans held for sale	0	0
Interest receivable	0	0
Derivative assets	0	3
Retained interests in securitizations	0	0
Financial liabilities:
Non-interest bearing deposits	25,388	22,643
Interest-bearing deposits	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	2,330	915
Other borrowings	0	0
Interest payable	0	0
Derivative liabilities	1	4
Level 2
Financial assets:
Cash and cash equivalents	0	0
Restricted cash for securitization investors	0	0
Securities available for sale	33,826	37,510
Securities held to maturity	22,770	18,895
Net loans held for investment	0	0
Loans held for sale	431	219
Interest receivable	1,268	1,418
Derivative assets	785	906
Retained interests in securitizations	0	0
Financial liabilities:
Non-interest bearing deposits	0	0
Interest-bearing deposits	11,341	14,346
Securitized debt obligations	10,654	10,835
Senior and subordinated notes	19,075	13,715
Federal funds purchased and securities loaned or sold under agreements to repurchase	0	0
Other borrowings	10,876	16,324
Interest payable	249	307
Derivative liabilities	329	668
Level 3
Financial assets:
Cash and cash equivalents	0	0
Restricted cash for securitization investors	0	0
Securities available for sale	1,466	3,330
Securities held to maturity	158	290
Net loans held for investment	201,441	198,138
Loans held for sale	0	0
Interest receivable	0	0
Derivative assets	51	50
Retained interests in securitizations	203	199
Financial liabilities:
Non-interest bearing deposits	0	0
Interest-bearing deposits	161,347	161,170
Securitized debt obligations	0	246
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
Derivative liabilities	39	38
Carrying Amount
Financial assets:
Cash and cash equivalents	6,148	6,291
Restricted cash for securitization investors	405	874
Securities available for sale	39,665	41,800
Securities held to maturity	22,182	19,132
Net loans held for investment	197,380	192,884
Loans held for sale	427	218
Interest receivable	1,268	1,418
Derivative assets	836	959
Retained interests in securitizations	203	199
Financial liabilities:
Non-interest bearing deposits	25,388	22,643
Interest-bearing deposits	178,876	181,880
Securitized debt obligations	10,508	10,289
Senior and subordinated notes	18,534	13,134
Federal funds purchased and securities loaned or sold under agreements to repurchase	2,330	915
Other borrowings	10,871	16,316
Interest payable	249	307
Derivative liabilities	369	710
Estimated Fair Value
Financial assets:
Cash and cash equivalents	6,148	6,291
Restricted cash for securitization investors	405	874
Securities available for sale	39,665	41,800
Securities held to maturity	22,928	19,185
Net loans held for investment	201,441	198,138
Loans held for sale	431	219
Interest receivable	1,268	1,418
Derivative assets	836	959
Retained interests in securitizations	203	199
Financial liabilities:
Non-interest bearing deposits	25,388	22,643
Interest-bearing deposits	172,688	175,516
Securitized debt obligations	10,654	11,081
Senior and subordinated notes	19,075	13,715
Federal funds purchased and securities loaned or sold under agreements to repurchase	2,330	915
Other borrowings	10,876	16,324
Interest payable	249	307
Derivative liabilities	$ 369	$ 710