Fair Value Measurements - Change in Fair Values of Level 3 Financial Instruments (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Other Investments [Member] | Principal Investments Direct [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 141	$ 191
Gains (Losses) Included in Earnings	4	(4)
Purchases		4
Sales	(4)
Settlements
Transfers into Level 3
Transfers out of Level 3
Ending Balance	141	191
Unrealized Gains (Losses) Included in Earnings	6	(4)
Other Investments [Member] | Principal Investments Indirect [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	413	436
Gains (Losses) Included in Earnings	20	12
Purchases	1	6
Sales	(31)	(19)
Settlements
Transfers into Level 3
Transfers out of Level 3
Ending Balance	403	435
Unrealized Gains (Losses) Included in Earnings	9	4
Other Investments [Member] | Equity and Mezzanine Investments Direct [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance
Gains (Losses) Included in Earnings
Purchases
Sales
Settlements
Transfers into Level 3
Transfers out of Level 3
Ending Balance
Unrealized Gains (Losses) Included in Earnings
Other Investments [Member] | Equity and Mezzanine Investments Indirect [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	23	41
Gains (Losses) Included in Earnings	(1)
Purchases
Sales
Settlements	(2)	(2)
Transfers into Level 3
Transfers out of Level 3
Ending Balance	20	39
Unrealized Gains (Losses) Included in Earnings	(1)
Trading Account Assets [Member] | Other Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance
Gains (Losses) Included in Earnings		1
Purchases
Sales
Settlements		(1)
Transfers into Level 3
Transfers out of Level 3
Ending Balance
Unrealized Gains (Losses) Included in Earnings		1
Trading Account Assets [Member] | States and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance		3
Gains (Losses) Included in Earnings
Purchases
Sales
Settlements
Transfers into Level 3
Transfers out of Level 3
Ending Balance		3
Unrealized Gains (Losses) Included in Earnings
Trading Account Assets [Member] | Other Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance
Gains (Losses) Included in Earnings		4
Purchases
Sales		(4)
Settlements
Transfers into Level 3
Transfers out of Level 3
Ending Balance
Unrealized Gains (Losses) Included in Earnings
Interest Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	25	19
Gains (Losses) Included in Earnings	1	(3)
Purchases	2
Sales	(1)	(1)
Settlements
Transfers into Level 3	3	14
Transfers out of Level 3	(8)	(2)
Ending Balance	22	27
Unrealized Gains (Losses) Included in Earnings
Commodity [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance		1
Gains (Losses) Included in Earnings		3
Purchases
Sales
Settlements
Transfers into Level 3
Transfers out of Level 3
Ending Balance		4
Unrealized Gains (Losses) Included in Earnings
Credit [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	3	4
Gains (Losses) Included in Earnings	(2)	(1)
Purchases
Sales
Settlements	2	1
Transfers into Level 3
Transfers out of Level 3
Ending Balance	3	4
Unrealized Gains (Losses) Included in Earnings