Derivative Instruments - Additional Information (Detail) (USD $)	3 Months Ended				9 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 Scenario, Forecast [Member]	Mar. 31, 2014 Scenario, Forecast [Member]
Derivative [Line Items]
Realized and unrealized losses on derivatives classified as cash flow hedges recorded in other comprehensive income (loss)	$ 371,000,000	$ 404,000,000	$ 455,000,000	$ 489,000,000
Estimated loss to be reclassified from other comprehensive income (loss) into earnings	(33,000,000)				(100,000,000)	(133,000,000)
Carrying amount of non-derivative debt instruments designated as net investment hedges	0	0
Fair value of derivatives under collateral agreements in a net liability position	1,300,000,000
Collateral posted by company netted against net liability position	1,100,000,000
Forward commitments to sell mortgage loans	14,400,000,000
Hedged mortgage loans held for sale	6,500,000,000
Unfunded mortgage loan commitments	$ 10,100,000,000