Other Expenses (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended	12 Months Ended
	Jun. 30, 2010	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Component of Operating Other Cost and Expense [Line Items]
Benefit on claims resolution		$ (362)	$ 0	$ 0
Aggregate pre-tax securities lending charge				414
Legal costs				9
One-time cash contribution to the SSgA lending funds				330
Net asset value per underlying cash collateral pools	$ 1
Reserve for decline in market value of collateral securities				75
Lehman Entities [Member]
Component of Operating Other Cost and Expense [Line Items]
Amount of bankruptcy claims			400
Proceeds from Legal Settlements, Number of Payments		2
Distributions received from bankruptcy claims		338
Benefit on claims resolution		(362)
Additional gain on claims resolution		$ 10