Fair Value Measurements - Additional Information Relating To Asset-Backed Securities and Collateralized Debt Obligations (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	$ 275	$ 448
Level 2 [Member] | Trading Securities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	234
Level 3 [Member] | Trading Securities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	260
Estimate of Fair Value Measurement [Member] | Trading Securities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	494
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	229
AAA - A Rating [Member] | Level 2 [Member] | Trading Securities [Member] | Student Loans [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	81
AAA - A Rating [Member] | Level 2 [Member] | Available for sale securities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	274
AAA - A Rating [Member] | Level 2 [Member] | Available for sale securities [Member] | Other [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	94
AAA - A Rating [Member] | Level 2 [Member] | Alt [Member] | Trading Securities [Member] | Residential Mortgage [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	89
AAA - A Rating [Member] | Level 2 [Member] | Alt [Member] | Available for sale securities [Member] | Home Equity Line of Credit [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	94
AAA - A Rating [Member] | Level 2 [Member] | Subprime [Member] | Trading Securities [Member] | Residential Mortgage [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	59
AAA - A Rating [Member] | Level 2 [Member] | Commercial Mortgages [Member] | Available for sale securities [Member] | Residential Mortgage [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	86
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	0
AAA - A Rating [Member] | Level 3 [Member] | Trading Securities [Member] | Student Loans [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	0
AAA - A Rating [Member] | Level 3 [Member] | Available for sale securities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	0
AAA - A Rating [Member] | Level 3 [Member] | Available for sale securities [Member] | Other [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	0
AAA - A Rating [Member] | Level 3 [Member] | Alt [Member] | Trading Securities [Member] | Residential Mortgage [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	0
AAA - A Rating [Member] | Level 3 [Member] | Alt [Member] | Available for sale securities [Member] | Home Equity Line of Credit [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	0
AAA - A Rating [Member] | Level 3 [Member] | Subprime [Member] | Trading Securities [Member] | Residential Mortgage [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	0
AAA - A Rating [Member] | Level 3 [Member] | Commercial Mortgages [Member] | Available for sale securities [Member] | Residential Mortgage [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	0
AAA - A Rating [Member] | Estimate of Fair Value Measurement [Member] | Trading Securities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	229
AAA - A Rating [Member] | Estimate of Fair Value Measurement [Member] | Trading Securities [Member] | Student Loans [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	81
AAA - A Rating [Member] | Estimate of Fair Value Measurement [Member] | Available for sale securities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	274
AAA - A Rating [Member] | Estimate of Fair Value Measurement [Member] | Available for sale securities [Member] | Other [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	94
AAA - A Rating [Member] | Estimate of Fair Value Measurement [Member] | Alt [Member] | Trading Securities [Member] | Residential Mortgage [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	89
AAA - A Rating [Member] | Estimate of Fair Value Measurement [Member] | Alt [Member] | Available for sale securities [Member] | Home Equity Line of Credit [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	94
AAA - A Rating [Member] | Estimate of Fair Value Measurement [Member] | Subprime [Member] | Trading Securities [Member] | Residential Mortgage [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	59
AAA - A Rating [Member] | Estimate of Fair Value Measurement [Member] | Commercial Mortgages [Member] | Available for sale securities [Member] | Residential Mortgage [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	86
BBB -B Rating [Member] | Level 2 [Member] | Trading Securities [Member] | Collateralized debt obligations [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	0
BBB -B Rating [Member] | Level 3 [Member] | Trading Securities [Member] | Collateralized debt obligations [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	260
BBB -B Rating [Member] | Estimate of Fair Value Measurement [Member] | Trading Securities [Member] | Collateralized debt obligations [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	260
CCC - Unrated [Member] | Level 2 [Member] | Available for sale securities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	275
CCC - Unrated [Member] | Level 2 [Member] | Alt [Member] | Available for sale securities [Member] | Residential Mortgage [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	1
CCC - Unrated [Member] | Level 2 [Member] | Subprime [Member] | Trading Securities [Member] | Residential Mortgage [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	5
CCC - Unrated [Member] | Level 3 [Member] | Available for sale securities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	0
CCC - Unrated [Member] | Level 3 [Member] | Alt [Member] | Available for sale securities [Member] | Residential Mortgage [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	0
CCC - Unrated [Member] | Level 3 [Member] | Subprime [Member] | Trading Securities [Member] | Residential Mortgage [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	0
CCC - Unrated [Member] | Estimate of Fair Value Measurement [Member] | Available for sale securities [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	275
CCC - Unrated [Member] | Estimate of Fair Value Measurement [Member] | Alt [Member] | Available for sale securities [Member] | Residential Mortgage [Member]
Fair Value Of Other Financial Instrument [Line Items]
Available-for-sale securities backed by collateral	1
CCC - Unrated [Member] | Estimate of Fair Value Measurement [Member] | Subprime [Member] | Trading Securities [Member] | Residential Mortgage [Member]
Fair Value Of Other Financial Instrument [Line Items]
Trading asset-backed securities and related collateral	$ 5