Fair Value Measurement and Fair Value of Financial Instruments - Carrying Amount and Estimated Fair Value of Certain Financial Instruments (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Assets
Cash and cash equivalents, Fair Value	$ 3,354	$ 5,491
Cash and cash equivalents, Carrying Amount	3,354	5,491
Securities held to maturity, Fair Value	891	1,135
Securities held to maturity, Carrying Amount	905	1,103
Loans held for investment, net of allowance for loan losses, Fair Value	65,964	59,613
Loans held for investment, net of allowance for loan losses, Carrying Amount	64,243	58,284
FDIC indemnification asset, Fair Value	131	151
FDIC indemnification asset, Carrying Amount	233	338
Other assets, Fair Value	2	3
Other assets, Carrying Amount	2	3
Liabilities
Deposits, Fair Value	77,512	74,524
Deposits, Carrying Amount	77,310	74,255
Commercial paper and other short-term borrowings, Fair Value	3,792	1,363
Commercial paper and other short-term borrowings, Carrying Amount	3,792	1,363
Long-term debt, Fair Value	6,184	5,861
Long-term debt, Carrying Amount	6,058	5,622
Off-Balance Sheet Instruments
Commitments to extend credit and standby and commercial letters of credit, Fair Value	277	262
Commitments to extend credit and standby and commercial letters of credit, Carrying Amount	277	262
Level 1 [Member]
Assets
Cash and cash equivalents, Fair Value	3,354	5,491
Level 2 [Member]
Assets
Securities held to maturity, Fair Value	891	1,135
Liabilities
Deposits, Fair Value	77,512	74,524
Commercial paper and other short-term borrowings, Fair Value	3,792	1,363
Long-term debt, Fair Value	6,184	5,861
Level 3 [Member]
Assets
Loans held for investment, net of allowance for loan losses, Fair Value	65,964	59,613
FDIC indemnification asset, Fair Value	131	151
Other assets, Fair Value	2	3
Off-Balance Sheet Instruments
Commitments to extend credit and standby and commercial letters of credit, Fair Value	$ 277	$ 262