Fair Value Measurement (Details 2) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013		Dec. 31, 2012
Assets:
Short-term investments	$ 761		$ 817
Other invested assets	126		212
Credit derivative assets	106		141
FG VIEs' assets, at fair value	2,515		2,688
Liabilities:
Credit derivative liabilities	2,027		1,934
FG VIEs' liabilities with recourse, at fair value	1,828		2,090
FG VIEs' liabilities without recourse, at fair value	1,047		1,051
Fair value measurement on recurring basis | Estimated Fair Value
Assets:
Fixed maturity securities	9,873		10,056
Short-term investments	761		817
Other invested assets	79	[1]	120	[1]
Credit derivative assets	106		141
FG VIEs' assets, at fair value	2,515		2,688
Other assets	67	[2]	65	[2]
Total assets carried at fair value	13,401		13,887
Liabilities:
Credit derivative liabilities	2,027		1,934
FG VIEs' liabilities with recourse, at fair value	1,828		2,090
FG VIEs' liabilities without recourse, at fair value	1,047		1,051
Total liabilities carried at fair value	4,902		5,075
Fair value measurement on recurring basis | Estimated Fair Value | U.S. government and agencies
Assets:
Fixed maturity securities	717		794
Fair value measurement on recurring basis | Estimated Fair Value | Obligations of state and political subdivisions
Assets:
Fixed maturity securities	5,249		5,631
Fair value measurement on recurring basis | Estimated Fair Value | Corporate securities
Assets:
Fixed maturity securities	1,345		1,010
Fair value measurement on recurring basis | Estimated Fair Value | RMBS
Assets:
Fixed maturity securities	1,120		1,266
Fair value measurement on recurring basis | Estimated Fair Value | CMBS
Assets:
Fixed maturity securities	523		520
Fair value measurement on recurring basis | Estimated Fair Value | Asset-backed securities
Assets:
Fixed maturity securities	614		531
Fair value measurement on recurring basis | Estimated Fair Value | Foreign government securities
Assets:
Fixed maturity securities	305		304
Fair value measurement on recurring basis | Level 1
Assets:
Fixed maturity securities	0		0
Short-term investments	516		446
Other invested assets	0	[1]	0	[1]
Credit derivative assets	0		0
FG VIEs' assets, at fair value	0		0
Other assets	24	[2]	24	[2]
Total assets carried at fair value	540		470
Liabilities:
Credit derivative liabilities	0		0
FG VIEs' liabilities with recourse, at fair value	0		0
FG VIEs' liabilities without recourse, at fair value	0		0
Total liabilities carried at fair value	0		0
Fair value measurement on recurring basis | Level 1 | U.S. government and agencies
Assets:
Fixed maturity securities	0		0
Fair value measurement on recurring basis | Level 1 | Obligations of state and political subdivisions
Assets:
Fixed maturity securities	0		0
Fair value measurement on recurring basis | Level 1 | Corporate securities
Assets:
Fixed maturity securities	0		0
Fair value measurement on recurring basis | Level 1 | RMBS
Assets:
Fixed maturity securities	0		0
Fair value measurement on recurring basis | Level 1 | CMBS
Assets:
Fixed maturity securities	0		0
Fair value measurement on recurring basis | Level 1 | Asset-backed securities
Assets:
Fixed maturity securities	0		0
Fair value measurement on recurring basis | Level 1 | Foreign government securities
Assets:
Fixed maturity securities	0		0
Fair value measurement on recurring basis | Level 2
Assets:
Fixed maturity securities	9,073		9,496
Short-term investments	245		371
Other invested assets	73	[1]	112	[1]
Credit derivative assets	0		0
FG VIEs' assets, at fair value	0		0
Other assets	11	[2]	5	[2]
Total assets carried at fair value	9,402		9,984
Liabilities:
Credit derivative liabilities	0		0
FG VIEs' liabilities with recourse, at fair value	0		0
FG VIEs' liabilities without recourse, at fair value	0		0
Total liabilities carried at fair value	0		0
Fair value measurement on recurring basis | Level 2 | U.S. government and agencies
Assets:
Fixed maturity securities	717		794
Fair value measurement on recurring basis | Level 2 | Obligations of state and political subdivisions
Assets:
Fixed maturity securities	5,208		5,596
Fair value measurement on recurring basis | Level 2 | Corporate securities
Assets:
Fixed maturity securities	1,213		1,010
Fair value measurement on recurring basis | Level 2 | RMBS
Assets:
Fixed maturity securities	833		1,047
Fair value measurement on recurring basis | Level 2 | CMBS
Assets:
Fixed maturity securities	523		520
Fair value measurement on recurring basis | Level 2 | Asset-backed securities
Assets:
Fixed maturity securities	274		225
Fair value measurement on recurring basis | Level 2 | Foreign government securities
Assets:
Fixed maturity securities	305		304
Fair value measurement on recurring basis | Level 3
Assets:
Fixed maturity securities	800		560
Short-term investments	0		0
Other invested assets	6	[1]	8	[1]
Credit derivative assets	106		141
FG VIEs' assets, at fair value	2,515		2,688
Other assets	32	[2]	36	[2]
Total assets carried at fair value	3,459		3,433
Liabilities:
Credit derivative liabilities	2,027		1,934
FG VIEs' liabilities with recourse, at fair value	1,828		2,090
FG VIEs' liabilities without recourse, at fair value	1,047		1,051
Total liabilities carried at fair value	4,902		5,075
Fair value measurement on recurring basis | Level 3 | U.S. government and agencies
Assets:
Fixed maturity securities	0		0
Fair value measurement on recurring basis | Level 3 | Obligations of state and political subdivisions
Assets:
Fixed maturity securities	41		35
Fair value measurement on recurring basis | Level 3 | Corporate securities
Assets:
Fixed maturity securities	132		0
Fair value measurement on recurring basis | Level 3 | RMBS
Assets:
Fixed maturity securities	287		219
Fair value measurement on recurring basis | Level 3 | CMBS
Assets:
Fixed maturity securities	0		0
Fair value measurement on recurring basis | Level 3 | Asset-backed securities
Assets:
Fixed maturity securities	340		306
Fair value measurement on recurring basis | Level 3 | Foreign government securities
Assets:
Fixed maturity securities	$ 0		$ 0

[1] Includes mortgage loans that are recorded at fair value on a non-recurring basis. At September 30, 2013 and December 31, 2012, such investments were carried at their fair value of $6 million and $7 million, respectively.

[2] Includes fair value of CCS and supplemental executive retirement plan assets.