Contingencies - Additional Information (Detail) (USD $)						9 Months Ended			12 Months Ended	9 Months Ended
	Sep. 13, 2011	Aug. 19, 2011	Sep. 30, 2012 Lower Limit	Sep. 30, 2012 Upper Limit	May 31, 2009 Trust Preferred Securities legalmatter	Sep. 30, 2012 Consent Order Potential Claims per Instance [Member] Lower Limit	Sep. 30, 2012 Consent Order Potential Claims per Instance [Member] Upper Limit	Mar. 08, 2011 Preferred Securities [Member]	Dec. 31, 2011 Potential Mortgage Servicing Settlement and Claims [Member]	Sep. 30, 2012 Potential Statutory Civil Penalty per Violation [Member] Lower Limit	Sep. 30, 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	$ 300,000,000
Contingent Receipt, Judgement Award for Damages		34,000,000
Contingent Payments	5,000,000
Contingent Receipt, Prejudgement Interest Award		6,000,000
Number of putative class actions					3
Amount sold of an asset that is now related to a loss contingency					690,000,000			80,000,000
Loss Contingency, Loss in Period									120,000,000
contingency loss, loss in period, after tax									81,000,000
Loss Contingency, Damages Sought, Value						$ 500	$ 125,000			$ 5,500	$ 11,000