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	Sep. 30, 2012		Dec. 31, 2011
Assets
Cash and cash equivalents	$ 2,972		$ 4,195
Held to maturity securities, Carrying Value	1,182		1,273
Loans held for investment, net of allowance for loan losses, Carrying value	53,785	[1]	51,823	[1]
FDIC indemnification asset, carrying value	401		598
Cash and cash equivalents, Fair Value	2,972		4,195
Held to maturity securities, Fair Value	1,224		1,429
Loans held for investment, net of allowance for loan losses, Fair Value	55,057		52,423	[1]
FDIC indemnification asset, Fair Value	249		409
Liabilities
Deposits	65,143		64,420
Commercial paper and other short-term borrowings, Carrying Value	2,091		3,683
Long-term debt	5,540		6,684
Deposits, Fair Value	65,393		64,420
Commercial paper and other short-term borrowings, Fair Value	2,091		3,684
Long-term debt, Fair Value	5,774		6,798
Off-Balance Sheet Instruments
Commitments to extend credit and standby and commercial letters of credit, Carrying amount	278		287
Commitments to extend credit and standby and commercial letters of credit, Fair value	278		287
Assets
Cash and cash equivalents	2,972		4,195
Held to maturity securities, Carrying Value	1,182		1,273
Loans held for investment, net of allowance for loan losses, Carrying value	53,785	[1]	51,823	[1]
FDIC indemnification asset, carrying value	401		598
Cash and cash equivalents, Fair Value	2,972		4,195
Held to maturity securities, Fair Value	1,224		1,429
Loans held for investment, net of allowance for loan losses, Fair Value	55,057		52,423	[1]
FDIC indemnification asset, Fair Value	249		409
Liabilities
Deposits	65,143		64,420
Commercial paper and other short-term borrowings, Carrying Value	2,091		3,683
Long-term debt	5,540		6,684
Deposits, Fair Value	65,393		64,420
Commercial paper and other short-term borrowings, Fair Value	2,091		3,684
Long-term debt, Fair Value	5,774		6,798
Off-Balance Sheet Instruments
Commitments to extend credit and standby and commercial letters of credit, Carrying amount	278		287
Commitments to extend credit and standby and commercial letters of credit, Fair value	278		287
Level 1 [Member]
Assets
Cash and cash equivalents, Fair Value	2,972
Assets
Cash and cash equivalents, Fair Value	2,972
Level 2 [Member]
Assets
Held to maturity securities, Fair Value	1,224
Liabilities
Deposits, Fair Value	65,393
Commercial paper and other short-term borrowings, Fair Value	2,091
Long-term debt, Fair Value	5,774
Assets
Held to maturity securities, Fair Value	1,224
Liabilities
Deposits, Fair Value	65,393
Commercial paper and other short-term borrowings, Fair Value	2,091
Long-term debt, Fair Value	5,774
Level 3 [Member]
Assets
Loans held for investment, net of allowance for loan losses, Fair Value	55,057
FDIC indemnification asset, Fair Value	249
Off-Balance Sheet Instruments
Commitments to extend credit and standby and commercial letters of credit, Fair value	278
Assets
Loans held for investment, net of allowance for loan losses, Fair Value	55,057
FDIC indemnification asset, Fair Value	249
Off-Balance Sheet Instruments
Commitments to extend credit and standby and commercial letters of credit, Fair value	$ 278

[1] Excludes lease financing, net of related allowance.