Contingencies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified							12 Months Ended	3 Months Ended
	Sep. 13, 2011	Aug. 19, 2011	Mar. 31, 2012 Lower Limit	Mar. 31, 2012 Upper Limit	May 31, 2009 Trust Preferred Securities legalmatter	Mar. 08, 2011 Preferred Securities [Member]	Dec. 31, 2011 Potential Mortgage Servicing Settlement and Claims [Member]	Mar. 31, 2012 Potential Statutory Civil Penalty per Violation [Member] Lower Limit	Mar. 31, 2012 Potential Statutory Civil Penalty per Violation [Member] Upper Limit
Aggregate range of reasonably possible losses on legal matters in excess of the accrued liability			$ 0	$ 250
Contingent Receipt, Judgement Award for Damages		34
Contingent Payments	5
Contingent Receipt, Prejudgement Interest Award		6
Number of putative class actions					3
Amount sold of an asset that is now related to a loss contingency					690	80
Loss Contingency, Loss in Period							120
contingency loss, loss in period, after tax							$ 81
Loss Contingency, Range of Possible Loss								5500	11000