Derivative Positions (Additional Information) (Detail) (Not Designated as Hedging Instrument [Member], USD $) In Millions, unless otherwise specified	1 Months Ended
	May 31, 2009	Mar. 31, 2015	Dec. 31, 2014
Trading Activity
Asset Amount Notional From Purchased And Written Interest Rate Swap Risk Participation Agreements		$ 7	$ 4
Notional Amount Liability Purchased And Written Interest Rate Swap Risk Participation Agreements		4
Derivative Financial Instruments, Assets | Trading Activity
Notional Amount Of Interest Rate Future Derivatives		10,400	10,300
Notional related to equity futures		554	563
Derivative Financial Instruments, Liabilities [Member]
Notional Amount Derivative Liability Sale Of Shares		49	49
Derivative Financial Instruments, Liabilities [Member] | Future [Member]
Notional Amount Of Interest Rate Future Derivatives		$ 576	$ 791
Derivative Financial Instruments, Liabilities [Member] | Visa Interest [Member]
Number Of Shares Sold To Selected Financial Institutions	3.2