Fair Value Measurements - Additional Information Relating To Asset-Backed Securities and Collateralized Debt Obligations (Detail) $ in Millions		Jun. 30, 2015 USD ($)
Level 2 [Member] | Trading Securities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	[1]	$ 217
Level 3 [Member] | Trading Securities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	[1]	240
AAA - A Rating [Member] | Level 2 [Member] | Trading Securities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	[1]	211
AAA - A Rating [Member] | Level 2 [Member] | Available-for-sale Securities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	[1]	204
AAA - A Rating [Member] | Level 3 [Member] | Trading Securities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	[1]	0
AAA - A Rating [Member] | Level 3 [Member] | Available-for-sale Securities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	[1]	0
Commercial mortgages [Member] | AAA - A Rating [Member] | Level 2 [Member] | Available-for-sale Securities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	[1]	27
Commercial mortgages [Member] | AAA - A Rating [Member] | Level 3 [Member] | Available-for-sale Securities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	[1]	0
Other [Member] | AAA - A Rating [Member] | Level 2 [Member] | Available-for-sale Securities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	[1]	94
Other [Member] | AAA - A Rating [Member] | Level 3 [Member] | Available-for-sale Securities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	[1]	0
Collateralized debt obligations [Member] | BBB -B Rating [Member] | Level 2 [Member] | Trading Securities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	[1]	0
Collateralized debt obligations [Member] | BBB -B Rating [Member] | Level 3 [Member] | Trading Securities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	[1]	240
Student loans [Member] | AAA - A Rating [Member] | Level 2 [Member] | Trading Securities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	[1]	88
Student loans [Member] | AAA - A Rating [Member] | Level 3 [Member] | Trading Securities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	[1]	0
Estimate of fair value [Member] | Trading Securities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	[1]	457
Estimate of fair value [Member] | AAA - A Rating [Member] | Trading Securities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	[1]	211
Estimate of fair value [Member] | AAA - A Rating [Member] | Available-for-sale Securities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	[1]	204
Estimate of fair value [Member] | Commercial mortgages [Member] | AAA - A Rating [Member] | Available-for-sale Securities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	[1]	27
Estimate of fair value [Member] | Other [Member] | AAA - A Rating [Member] | Available-for-sale Securities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	[1]	94
Estimate of fair value [Member] | Collateralized debt obligations [Member] | BBB -B Rating [Member] | Trading Securities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	[1]	240
Estimate of fair value [Member] | Student loans [Member] | AAA - A Rating [Member] | Trading Securities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	[1]	88
Alt [Member] | Home Equity [Member] | AAA - A Rating [Member] | Level 2 [Member] | Available-for-sale Securities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	[1]	83
Alt [Member] | Home Equity [Member] | AAA - A Rating [Member] | Level 3 [Member] | Available-for-sale Securities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	[1]	0
Alt [Member] | Residential Mortgages [Member] | AAA - A Rating [Member] | Level 2 [Member] | Trading Securities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	[1]	73
Alt [Member] | Residential Mortgages [Member] | AAA - A Rating [Member] | Level 3 [Member] | Trading Securities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	[1]	0
Alt [Member] | Estimate of fair value [Member] | Home Equity [Member] | AAA - A Rating [Member] | Available-for-sale Securities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	[1]	83
Alt [Member] | Estimate of fair value [Member] | Residential Mortgages [Member] | AAA - A Rating [Member] | Trading Securities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	[1]	73
Subprime [Member] | Residential Mortgages [Member] | AAA - A Rating [Member] | Level 2 [Member] | Trading Securities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	[1]	50
Subprime [Member] | Residential Mortgages [Member] | AAA - A Rating [Member] | Level 3 [Member] | Trading Securities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	[1]	0
Subprime [Member] | Residential Mortgages [Member] | CCC - Unrated [Member] | Level 2 [Member] | Trading Securities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	[1]	6
Subprime [Member] | Residential Mortgages [Member] | CCC - Unrated [Member] | Level 3 [Member] | Trading Securities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	[1]	0
Subprime [Member] | Estimate of fair value [Member] | Residential Mortgages [Member] | AAA - A Rating [Member] | Trading Securities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	[1]	50
Subprime [Member] | Estimate of fair value [Member] | Residential Mortgages [Member] | CCC - Unrated [Member] | Trading Securities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	[1]	$ 6

[1] We utilize S&P as the primary source of credit ratings in the tables above. If S&P ratings are not available, ratings by Moody's and Fitch are used in that order. Ratings for collateralized debt obligations represent the ratings associated with the underlying collateral.