Securities - Realized gains and losses on investment securities Transactions Attributable to available-for-sale securities (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Investments, Debt and Equity Securities [Abstract]
Gross realized gains, Available-for-sale securities	$ 83	$ 132	$ 207	$ 201
Gross realized losses, Available-for-sale securities	(60)	(67)	(61)	(106)
Net realized gains, Available-for-sale securities	23	65	146	95
Gross realized gains, Held-to-maturity securities	0	0	8	0
Gross realized losses, Held-to-maturity securities	0	0	0	0
Net realized gain (losses), Held-to-maturity securities	$ 0	$ 0	$ 8	$ 0