Commitments and Contingencies - Commitments and Contingencies (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012
Contingencies And Commitments [Line Items]
2013	$ 1,341
2014	2,591
2015	3,997
2016	3,457
2017	2,796
Thereafter	3,901
Unfunded financing commitments	$ 18,083