Netting Arrangements for Certain Financial Instruments and Securities Financing Activities - Information on Company's Accounting Netting Adjustments and Items Not Offset in Consolidated Balance Sheet Assets But Available for Offset in Event of Default (Detail) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Offsetting [Abstract]
Derivative assets Gross Recognized Assets	$ 2,174	$ 1,847
Reverse repurchase agreements Gross Recognized Assets	133	40
Securities borrowed Gross Recognized Assets	717	638
Total Gross Recognized Assets	3,024	2,525
Derivative assets Gross amounts assets offset in consolidated balance sheet	(932)	(870)
Total Gross amounts assets offset in consolidated balance sheet	(932)	(870)
Derivative assets Net Amounts Presented in the Consolidated Balance Sheet	1,242	977
Reverse repurchase agreements Net Amounts Presented in the Consolidated Balance Sheet	133	40
Securities borrowed Net Amounts Presented in the Consolidated Balance Sheet	717	638
Total Net Amounts Presented in the Consolidated Balance Sheet	2,092	1,655
Derivative assets Gross Amounts Not Offset Consolidated Balance Financial Instruments	(115)	(58)
Reverse repurchase agreements Gross financial instrument asset amounts not offset in consolidated balance sheet	(42)	(40)
Securities borrowed Gross financial instrument asset amounts not offset in consolidated balance sheet	0	0
Total Gross financial instrument asset amounts not offset in consolidated balance sheet	(157)	(98)
Reverse repurchase agreements Gross collateral received amounts not offset in consolidated balance sheet	(91)
Securities borrowed Gross collateral received amounts not offset in consolidated balance sheet	(696)	(620)
Total Gross collateral received amounts not offset in consolidated balance sheet	(787)	(620)
Derivative assets Net Amount	1,127	919
Reverse repurchase agreements Net Amount	0	0
Securities borrowed Net Amount	21	18
Total Net Amount Assets	$ 1,148	$ 937