Fair Value Measurement (Details 2) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011
Assets:
Short-term investments	$ 564		$ 734
Other invested assets	205		223
Credit Risk Derivative Assets, at Fair Value	450		469
FG VIEs' assets, at fair value	2,693		2,819
Liabilities:
Credit Risk Derivative Liabilities, at Fair Value	2,151		1,773
FG VIEs' liabilities with recourse, at fair value	2,169		2,397
FG VIEs' liabilities without recourse, at fair value	1,018		1,061
Fair value measurement on recurring basis | Estimated Fair Value
Assets:
Available-for-sale Securities, Fair Value Disclosure	10,318		10,142
Short-term investments	564		734
Other invested assets	103	[1]	43	[1]
Credit Risk Derivative Assets, at Fair Value	450		469
FG VIEs' assets, at fair value	2,693		2,819
Other assets	71	[2]	80	[2]
Total assets carried at fair value	14,199		14,287
Liabilities:
Credit Risk Derivative Liabilities, at Fair Value	2,151		1,773
FG VIEs' liabilities with recourse, at fair value	2,169		2,397
FG VIEs' liabilities without recourse, at fair value	1,018		1,061
Total liabilities carried at fair value	5,338		5,231
Fair value measurement on recurring basis | Estimated Fair Value | U.S. government and agencies
Assets:
Available-for-sale Securities, Fair Value Disclosure	810		922
Fair value measurement on recurring basis | Estimated Fair Value | Obligations of state and political subdivisions
Assets:
Available-for-sale Securities, Fair Value Disclosure	5,714		5,456
Fair value measurement on recurring basis | Estimated Fair Value | Corporate securities
Assets:
Available-for-sale Securities, Fair Value Disclosure	1,030		1,038
Fair value measurement on recurring basis | Estimated Fair Value | RMBS
Assets:
Available-for-sale Securities, Fair Value Disclosure	1,384		1,428
Fair value measurement on recurring basis | Estimated Fair Value | CMBS
Assets:
Available-for-sale Securities, Fair Value Disclosure	513		500
Fair value measurement on recurring basis | Estimated Fair Value | Asset-backed securities
Assets:
Available-for-sale Securities, Fair Value Disclosure	561		458
Fair value measurement on recurring basis | Estimated Fair Value | Foreign government securities
Assets:
Available-for-sale Securities, Fair Value Disclosure	306		340
Fair value measurement on recurring basis | Level 2
Assets:
Available-for-sale Securities, Fair Value Disclosure	9,799		9,763
Short-term investments	296		524
Other invested assets	95	[1]	32	[1]
Credit Risk Derivative Assets, at Fair Value	0		0
FG VIEs' assets, at fair value	0		0
Other assets	5	[2]	0	[2]
Total assets carried at fair value	10,195		10,319
Liabilities:
Credit Risk Derivative Liabilities, at Fair Value	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
Other Investments Fair Value Disclosure	95
Fair value measurement on recurring basis | Level 2 | U.S. government and agencies
Assets:
Available-for-sale Securities, Fair Value Disclosure	810		922
Fair value measurement on recurring basis | Level 2 | Obligations of state and political subdivisions
Assets:
Available-for-sale Securities, Fair Value Disclosure	5,703		5,446
Fair value measurement on recurring basis | Level 2 | Corporate securities
Assets:
Available-for-sale Securities, Fair Value Disclosure	1,030		1,038
Fair value measurement on recurring basis | Level 2 | RMBS
Assets:
Available-for-sale Securities, Fair Value Disclosure	1,175		1,294
Fair value measurement on recurring basis | Level 2 | CMBS
Assets:
Available-for-sale Securities, Fair Value Disclosure	513		500
Fair value measurement on recurring basis | Level 2 | Asset-backed securities
Assets:
Available-for-sale Securities, Fair Value Disclosure	262		223
Fair value measurement on recurring basis | Level 2 | Foreign government securities
Assets:
Available-for-sale Securities, Fair Value Disclosure	306		340
Fair value measurement on recurring basis | Level 3
Assets:
Available-for-sale Securities, Fair Value Disclosure	519		379
Short-term investments	0		0
Other invested assets	8	[1]	11	[1]
Credit Risk Derivative Assets, at Fair Value	450		469
FG VIEs' assets, at fair value	2,693		2,819
Other assets	42	[2]	54	[2]
Total assets carried at fair value	3,712		3,732
Liabilities:
Credit Risk Derivative Liabilities, at Fair Value	2,151		1,773
FG VIEs' liabilities with recourse, at fair value	2,169		2,397
FG VIEs' liabilities without recourse, at fair value	1,018		1,061
Total liabilities carried at fair value	5,338		5,231
Other Investments Fair Value Disclosure	1
Fair value measurement on recurring basis | Level 3 | U.S. government and agencies
Assets:
Available-for-sale Securities, Fair Value Disclosure	0		0
Fair value measurement on recurring basis | Level 3 | Obligations of state and political subdivisions
Assets:
Available-for-sale Securities, Fair Value Disclosure	11		10
Fair value measurement on recurring basis | Level 3 | Corporate securities
Assets:
Available-for-sale Securities, Fair Value Disclosure	0		0
Fair value measurement on recurring basis | Level 3 | RMBS
Assets:
Available-for-sale Securities, Fair Value Disclosure	209		134
Fair value measurement on recurring basis | Level 3 | CMBS
Assets:
Available-for-sale Securities, Fair Value Disclosure	0		0
Fair value measurement on recurring basis | Level 3 | Asset-backed securities
Assets:
Available-for-sale Securities, Fair Value Disclosure	299		235
Fair value measurement on recurring basis | Level 3 | Foreign government securities
Assets:
Available-for-sale Securities, Fair Value Disclosure	0		0
Fair value measurement on recurring basis | Level 1
Assets:
Available-for-sale Securities, Fair Value Disclosure	0		0
Short-term investments	268		210
Other invested assets	0	[1]	0	[1]
Credit Risk Derivative Assets, at Fair Value	0		0
FG VIEs' assets, at fair value	0		0
Other assets	24	[2]	26	[2]
Total assets carried at fair value	292		236
Liabilities:
Credit Risk Derivative Liabilities, at Fair Value	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:
Available-for-sale Securities, Fair Value Disclosure	0		0
Fair value measurement on recurring basis | Level 1 | Obligations of state and political subdivisions
Assets:
Available-for-sale Securities, Fair Value Disclosure	0		0
Fair value measurement on recurring basis | Level 1 | Corporate securities
Assets:
Available-for-sale Securities, Fair Value Disclosure	0		0
Fair value measurement on recurring basis | Level 1 | RMBS
Assets:
Available-for-sale Securities, Fair Value Disclosure	0		0
Fair value measurement on recurring basis | Level 1 | CMBS
Assets:
Available-for-sale Securities, Fair Value Disclosure	0		0
Fair value measurement on recurring basis | Level 1 | Asset-backed securities
Assets:
Available-for-sale Securities, Fair Value Disclosure	0		0
Fair value measurement on recurring basis | Level 1 | Foreign government securities
Assets:
Available-for-sale Securities, Fair Value Disclosure	0		0
Fair value measurement on non-recurring basis | Level 3
Liabilities:
Mortgage loans recorded at fair value	$ 7		$ 9

[1] Includes mortgage loans that are recorded at fair value on a non-recurring basis. At September 30, 2012 and December 31, 2011, such investments were carried at their market value of $7 million and $9 million, respectively.

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