Derivative Instruments - Additional Information (Detail) (USD $)			9 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013	Dec. 31, 2014 Scenario, Forecast [Member]	Mar. 31, 2015 Scenario, Forecast [Member]
Derivative [Line Items]
Realized and unrealized losses on derivatives classified as cash flow hedges recorded in other comprehensive income (loss)	$ 238,000,000	$ 261,000,000
Estimated loss to be reclassified from other comprehensive income (loss) into earnings			88,000,000	119,000,000
Forward commitments to sell mortgage loans	4,500,000,000
Hedged mortgage loans held for sale	1,500,000,000
Unfunded mortgage loan commitments	3,800,000,000
Fair value of derivatives under collateral agreements in a net liability position	965,000,000
Collateral posted by company netted against net liability position	$ 804,000,000