Derivative Instruments - Narrative (Detail) (USD $)	Sep. 30, 2012	Dec. 31, 2011
Derivative Instruments:
Interest rate swaps - weighted average pay rate, percentage	2.23%	2.55%
Interest rate swaps - weighted average receive rate, percentage	0.27%	0.33%
Interest rate swaps, gross unrealized loss	$ 2,900,000,000	$ 2,600,000,000
Interest rate swaps, notional amount related to gross unrealized loss	46,200,000,000	40,100,000,000
Interest rate swaps, gross unrealized gain	10,500,000
Interest rate swaps, notional amount related to gross unrealized gain	500,000,000
Derivative instruments with credit-risk-related, net liability position, aggregate fair value	$ 3,000,000,000