Derivative Financial Instruments (Details 2) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Asset derivatives
Asset derivatives gross amount	$ 244	$ 169
Liability derivatives
Liability derivatives gross amount	(738)	(664)
OTC derivatives
Asset derivatives
Asset derivatives gross amount	57	52
Offsets of derivative assets under counterparty netting	(33)	(29)
Derivative asset offsets under cash collateral received	(14)	(18)
Derivative assets net amount on balance sheet	10	5
Derivative assets pledged under securities collateral	(10)	(5)
Liability derivatives
Liability derivatives gross amount	(53)	(63)
Offsets of derivative liabilities under counterparty netting	33	29
Derivative liability offsets under cash collateral pledged	(9)
Derivative liabilities net amount on balance sheet	(29)	(34)
Derivative liabilities received under securities collateral	26	25
Derivative liabilities net amount	$ (3)	$ (9)