Derivative Financial Instruments (Details 6) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2013 entity	Dec. 31, 2012
Derivative Financial Instruments
Term of credit default swaps (in years)	5 years
The number of reference entities generally included in a CDX index	125
Credit Derivatives
Notional amount	$ 9,379	$ 16,179
Credit default swaps
Credit Derivatives
Notional amount	295	593
Fair value	(13)	(27)
Credit default swaps | Single name
Credit Derivatives
Notional amount		193
Fair value		(3)
Credit default swaps | Single name | Investment grade corporate debt
Credit Derivatives
Notional amount	115	168
Fair value	2
Credit default swaps | Single name | Municipal
Credit Derivatives
Notional amount		25
Fair value		(3)
Credit default swaps | First-to-default | Municipal
Credit Derivatives
Notional amount	100	100
Fair value	(16)	(26)
Credit default swaps | Index | Investment grade corporate debt
Credit Derivatives
Notional amount	80	300
Fair value	1	2
AAA | Credit default swaps
Credit Derivatives
Notional amount		5
AAA | Credit default swaps | Single name
Credit Derivatives
Notional amount		5
AAA | Credit default swaps | Single name | Investment grade corporate debt
Credit Derivatives
Notional amount		5
AA | Credit default swaps
Credit Derivatives
Notional amount	21	48
AA | Credit default swaps | Single name
Credit Derivatives
Notional amount		45
AA | Credit default swaps | Single name | Investment grade corporate debt
Credit Derivatives
Notional amount	20	20
AA | Credit default swaps | Single name | Municipal
Credit Derivatives
Notional amount		25
AA | Credit default swaps | Index | Investment grade corporate debt
Credit Derivatives
Notional amount	1	3
A | Credit default swaps
Credit Derivatives
Notional amount	150	232
A | Credit default swaps | Single name
Credit Derivatives
Notional amount		53
A | Credit default swaps | Single name | Investment grade corporate debt
Credit Derivatives
Notional amount	30	53
A | Credit default swaps | First-to-default | Municipal
Credit Derivatives
Notional amount	100	100
A | Credit default swaps | Index | Investment grade corporate debt
Credit Derivatives
Notional amount	20	79
BBB | Credit default swaps
Credit Derivatives
Notional amount	120	284
BBB | Credit default swaps | Single name
Credit Derivatives
Notional amount		80
BBB | Credit default swaps | Single name | Investment grade corporate debt
Credit Derivatives
Notional amount	65	80
BBB | Credit default swaps | Index | Investment grade corporate debt
Credit Derivatives
Notional amount	55	204
BB and lower | Credit default swaps
Credit Derivatives
Notional amount	4	24
BB and lower | Credit default swaps | Single name
Credit Derivatives
Notional amount		10
BB and lower | Credit default swaps | Single name | Investment grade corporate debt
Credit Derivatives
Notional amount		10
BB and lower | Credit default swaps | Index | Investment grade corporate debt
Credit Derivatives
Notional amount	$ 4	$ 14