Loans - High LTV Interest-only and Arm Loans (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Dec. 31, 2012
Loans [Line Items]
Residential mortgage loans with high LTV and no mortgage insurance	$ 900	[1]	$ 900	[1]
Sub-prime residential mortgage [Member]
Loans [Line Items]
Residential mortgage loans with high LTV and no mortgage insurance	19		20
Sub-prime residential mortgage loans held for sale excluded from Arm Loan	18		19
Amount of ARM loans to experience first interest rate reset in 2013	232
Amount of ARM loans to experience first interest rate reset in 2014	$ 327

[1] Residential mortgage loans with high LTV and no mortgage insurance includes both fixed rate and adjustable rate mortgages. Excludes $19 million and $20 million of subprime residential mortgage loans held for sale at March 31, 2013 and December 31, 2012, respectively.