Derivatives (Credit Risk on Freestanding Derivatives) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Credit Derivatives [Line Items]
Estimated Fair Value of Derivatives in Net Liability Position	$ 808	$ 850
Estimated Fair Value Of Incremental Collateral Provided Upon A One Notch Downgrade In The Company's Credit Rating	20	35
Estimated Fair Value Of Incremental Collateral Provided Upon A Downgrade In The Company's Credit Rating to a Level that Triggers Full Overnight Collateralization or Termination of the Derivative Position	24	73
Fixed Maturities [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Collateral Provided	879	875
Cash [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Collateral Provided	3	1
Derivatives Subject To Credit-Contingent Provisions [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Derivatives in Net Liability Position	729	771
Estimated Fair Value Of Incremental Collateral Provided Upon A One Notch Downgrade In The Company's Credit Rating	20	35
Estimated Fair Value Of Incremental Collateral Provided Upon A Downgrade In The Company's Credit Rating to a Level that Triggers Full Overnight Collateralization or Termination of the Derivative Position	24	73
Derivatives Subject To Credit-Contingent Provisions [Member] | Fixed Maturities [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Collateral Provided	737	775
Derivatives Subject To Credit-Contingent Provisions [Member] | Cash [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Collateral Provided	0	0
Derivatives Not Subject To Credit-Contingent Provisions [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Derivatives in Net Liability Position	79	79
Estimated Fair Value Of Incremental Collateral Provided Upon A One Notch Downgrade In The Company's Credit Rating	0	0
Estimated Fair Value Of Incremental Collateral Provided Upon A Downgrade In The Company's Credit Rating to a Level that Triggers Full Overnight Collateralization or Termination of the Derivative Position	0	0
Derivatives Not Subject To Credit-Contingent Provisions [Member] | Fixed Maturities [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Collateral Provided	142	100
Derivatives Not Subject To Credit-Contingent Provisions [Member] | Cash [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Collateral Provided	$ 3	$ 1