Loans Held for Investment portfolio and Related Allowance for Loan and Lease Losses (Detail) (USD $)	Mar. 31, 2015		Dec. 31, 2014		Mar. 31, 2014	Dec. 31, 2013
Individually evaluated	$ 2,767,000,000		$ 2,781,000,000
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	298,000,000		319,000,000
Collectively evaluated	129,345,000,000		130,059,000,000
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	1,595,000,000		1,618,000,000
Total evaluated	132,112,000,000		132,840,000,000
Loans And Leases Receivable Allowance Loans Evaluated For Impairment Excluding Fair Value Loans	1,893,000,000		1,937,000,000
Loans Receivable, Fair Value Disclosure	268,000,000		272,000,000
Total	132,380,000,000	[1]	133,112,000,000	[1]
Loans and Leases Receivable, Allowance	1,893,000,000		1,937,000,000		2,040,000,000	2,044,000,000
Commercial Portfolio Segment [Member]
Individually evaluated	80,000,000		92,000,000
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	6,000,000		11,000,000
Collectively evaluated	73,367,000,000		73,300,000,000
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	970,000,000		975,000,000
Total evaluated	73,447,000,000		73,392,000,000
Loans And Leases Receivable Allowance Loans Evaluated For Impairment Excluding Fair Value Loans	976,000,000		986,000,000
Loans Receivable, Fair Value Disclosure	0		0
Total	73,447,000,000		73,392,000,000
Loans and Leases Receivable, Allowance	976,000,000		986,000,000		966,000,000	946,000,000
Residential Portfolio Segment [Member]
Individually evaluated	2,561,000,000		2,563,000,000
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	285,000,000		300,000,000
Collectively evaluated	35,616,000,000		35,940,000,000
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	458,000,000		477,000,000
Total evaluated	38,177,000,000		38,503,000,000
Loans And Leases Receivable Allowance Loans Evaluated For Impairment Excluding Fair Value Loans	743,000,000		777,000,000
Loans Receivable, Fair Value Disclosure	268,000,000		272,000,000
Total	38,445,000,000		38,775,000,000
Loans and Leases Receivable, Allowance	743,000,000		777,000,000		910,000,000	930,000,000
Consumer Portfolio Segment [Member]
Individually evaluated	126,000,000		126,000,000
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	7,000,000		8,000,000
Collectively evaluated	20,362,000,000		20,819,000,000
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	167,000,000		166,000,000
Total evaluated	20,488,000,000		20,945,000,000
Loans And Leases Receivable Allowance Loans Evaluated For Impairment Excluding Fair Value Loans	174,000,000		174,000,000
Loans Receivable, Fair Value Disclosure	0		0
Total	20,488,000,000		20,945,000,000
Loans and Leases Receivable, Allowance	$ 174,000,000		$ 174,000,000		$ 164,000,000	$ 168,000,000

[1] Includes loans of consolidated VIEs of $277 million and $288 million at March 31, 2015 and December 31, 2014, respectively.