Derivative Financial Instruments and Off-balance sheet Financial Instruments (Details 5) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012 entity	Dec. 31, 2012 Credit default swaps	Dec. 31, 2011 Credit default swaps	Dec. 31, 2012 Credit default swaps Single name	Dec. 31, 2011 Credit default swaps Single name	Dec. 31, 2012 Credit default swaps Single name Investment grade corporate debt	Dec. 31, 2011 Credit default swaps Single name Investment grade corporate debt	Dec. 31, 2011 Credit default swaps Single name High yield debt	Dec. 31, 2012 Credit default swaps Single name Municipal	Dec. 31, 2011 Credit default swaps Single name Municipal	Dec. 31, 2012 Credit default swaps Baskets	Dec. 31, 2011 Credit default swaps Baskets	Dec. 31, 2011 Credit default swaps Tranche Investment grade corporate debt	Dec. 31, 2012 Credit default swaps First-to-default Municipal	Dec. 31, 2011 Credit default swaps First-to-default Municipal	Dec. 31, 2012 Credit default swaps Index Investment grade corporate debt	Dec. 31, 2012 AAA Credit default swaps	Dec. 31, 2012 AAA Credit default swaps Single name	Dec. 31, 2012 AAA Credit default swaps Single name Investment grade corporate debt	Dec. 31, 2012 AA Credit default swaps	Dec. 31, 2011 AA Credit default swaps	Dec. 31, 2012 AA Credit default swaps Single name	Dec. 31, 2011 AA Credit default swaps Single name	Dec. 31, 2012 AA Credit default swaps Single name Investment grade corporate debt	Dec. 31, 2011 AA Credit default swaps Single name Investment grade corporate debt	Dec. 31, 2012 AA Credit default swaps Single name Municipal	Dec. 31, 2011 AA Credit default swaps Single name Municipal	Dec. 31, 2012 AA Credit default swaps Index Investment grade corporate debt	Dec. 31, 2012 A Credit default swaps	Dec. 31, 2011 A Credit default swaps	Dec. 31, 2012 A Credit default swaps Single name	Dec. 31, 2011 A Credit default swaps Single name	Dec. 31, 2012 A Credit default swaps Single name Investment grade corporate debt	Dec. 31, 2011 A Credit default swaps Single name Investment grade corporate debt	Dec. 31, 2012 A Credit default swaps Baskets	Dec. 31, 2011 A Credit default swaps Baskets	Dec. 31, 2012 A Credit default swaps First-to-default Municipal	Dec. 31, 2011 A Credit default swaps First-to-default Municipal	Dec. 31, 2012 A Credit default swaps Index Investment grade corporate debt	Dec. 31, 2012 BBB Credit default swaps	Dec. 31, 2011 BBB Credit default swaps	Dec. 31, 2012 BBB Credit default swaps Single name	Dec. 31, 2011 BBB Credit default swaps Single name	Dec. 31, 2012 BBB Credit default swaps Single name Investment grade corporate debt	Dec. 31, 2011 BBB Credit default swaps Single name Investment grade corporate debt	Dec. 31, 2012 BBB Credit default swaps Index Investment grade corporate debt	Dec. 31, 2012 BB and lower Credit default swaps	Dec. 31, 2011 BB and lower Credit default swaps	Dec. 31, 2012 BB and lower Credit default swaps Single name	Dec. 31, 2011 BB and lower Credit default swaps Single name	Dec. 31, 2012 BB and lower Credit default swaps Single name Investment grade corporate debt	Dec. 31, 2011 BB and lower Credit default swaps Single name Investment grade corporate debt	Dec. 31, 2011 BB and lower Credit default swaps Single name High yield debt	Dec. 31, 2011 BB and lower Credit default swaps Baskets	Dec. 31, 2011 BB and lower Credit default swaps Tranche Investment grade corporate debt	Dec. 31, 2012 BB and lower Credit default swaps Index Investment grade corporate debt
Derivative Financial Instruments and Off-balance sheet Financial Instruments
Term of credit default swaps (in years)	P5Y
The number of reference entities generally included in a CDX index	125
Credit Derivatives
Notional amount		$ 593	$ 670	$ 193	$ 505	$ 168	$ 368	$ 2	$ 25	$ 135	$ 100	$ 165	$ 65	$ 100	$ 100	$ 300	$ 5	$ 5	$ 5	$ 48	$ 225	$ 45	$ 225	$ 20	$ 90	$ 25	$ 135	$ 3	$ 232	$ 188	$ 53	$ 88	$ 53	$ 88	$ 100	$ 100	$ 100	$ 100	$ 79	$ 284	$ 160	$ 80	$ 160	$ 80	$ 160	$ 204	$ 24	$ 97	$ 10	$ 32	$ 10	$ 30	$ 2	$ 65	$ 65	$ 14
Fair value		$ (27)	$ (81)	$ (3)	$ (19)		$ (7)		$ (3)	$ (12)	$ (26)	$ (62)	$ (29)	$ (26)	$ (33)	$ 2