Fair Value Measurement (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013 Security		Dec. 31, 2012
Assets:
Short-term investments	$ 729		$ 817
Other invested assets	148		212
Credit derivative assets	125		141
FG VIEs' assets, at fair value	2,813		2,688
Liabilities:
Credit derivative liabilities	2,518		1,934
FG VIEs' liabilities with recourse, at fair value	2,071		2,090
FG VIEs' liabilities without recourse, at fair value	1,107		1,051
Number of fixed maturity securities valued using model processes	35
Percentage of fixed maturity securities valued using model processes to the Company's fixed-income securities and short-term investments at fair value	5.10%
Fair value measurement on recurring basis | Estimated Fair Value
Assets:
Fixed maturity securities	9,985		10,056	[1]
Short-term investments	729		817
Other invested assets	80	[2]	120	[2]
Credit derivative assets	125		141
FG VIEs' assets, at fair value	2,813		2,688
Other assets	58	[3]	65	[3]
Total assets carried at fair value	13,790		13,887
Liabilities:
Credit derivative liabilities	2,518		1,934
FG VIEs' liabilities with recourse, at fair value	2,071		2,090
FG VIEs' liabilities without recourse, at fair value	1,107		1,051
Total liabilities carried at fair value	5,696		5,075
Fair value measurement on recurring basis | Estimated Fair Value | U.S. government and agencies
Assets:
Fixed maturity securities	877		794
Fair value measurement on recurring basis | Estimated Fair Value | Obligations of state and political subdivisions
Assets:
Fixed maturity securities	5,602		5,631
Fair value measurement on recurring basis | Estimated Fair Value | Corporate securities
Assets:
Fixed maturity securities	1,040		1,010
Fair value measurement on recurring basis | Estimated Fair Value | RMBS
Assets:
Fixed maturity securities	1,196		1,266
Fair value measurement on recurring basis | Estimated Fair Value | CMBS
Assets:
Fixed maturity securities	505		520
Fair value measurement on recurring basis | Estimated Fair Value | Asset-backed securities
Assets:
Fixed maturity securities	495		531
Fair value measurement on recurring basis | Estimated Fair Value | Foreign government securities
Assets:
Fixed maturity securities	270		304
Fair value measurement on recurring basis | Level 1
Assets:
Fixed maturity securities	0		0	[1]
Short-term investments	562		446
Other invested assets	0	[2]	0	[2]
Credit derivative assets	0		0
FG VIEs' assets, at fair value	0		0
Other assets	27	[3]	24	[3]
Total assets carried at fair value	589		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	9,443		9,496	[1]
Short-term investments	167		371
Other invested assets	73	[2]	112	[2]
Credit derivative assets	0		0
FG VIEs' assets, at fair value	0		0
Other assets	5	[3]	5	[3]
Total assets carried at fair value	9,688		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
Other investments	73
Fair value measurement on recurring basis | Level 2 | U.S. government and agencies
Assets:
Fixed maturity securities	877		794
Fair value measurement on recurring basis | Level 2 | Obligations of state and political subdivisions
Assets:
Fixed maturity securities	5,567		5,596
Fair value measurement on recurring basis | Level 2 | Corporate securities
Assets:
Fixed maturity securities	1,040		1,010
Fair value measurement on recurring basis | Level 2 | RMBS
Assets:
Fixed maturity securities	975		1,047
Fair value measurement on recurring basis | Level 2 | CMBS
Assets:
Fixed maturity securities	505		520
Fair value measurement on recurring basis | Level 2 | Asset-backed securities
Assets:
Fixed maturity securities	209		225
Fair value measurement on recurring basis | Level 2 | Foreign government securities
Assets:
Fixed maturity securities	270		304
Fair value measurement on recurring basis | Level 3
Assets:
Fixed maturity securities	542		560	[1]
Short-term investments	0		0
Other invested assets	7	[2]	8	[2]
Credit derivative assets	125		141
FG VIEs' assets, at fair value	2,813		2,688
Other assets	26	[3]	36	[3]
Total assets carried at fair value	3,513		3,433
Liabilities:
Credit derivative liabilities	2,518		1,934
FG VIEs' liabilities with recourse, at fair value	2,071		2,090
FG VIEs' liabilities without recourse, at fair value	1,107		1,051
Total liabilities carried at fair value	5,696		5,075
Other investments	1
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	35		35
Fair value measurement on recurring basis | Level 3 | Corporate securities
Assets:
Fixed maturity securities	0		0
Fair value measurement on recurring basis | Level 3 | RMBS
Assets:
Fixed maturity securities	221		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	286		306
Fair value measurement on recurring basis | Level 3 | Foreign government securities
Assets:
Fixed maturity securities	0		0
Fair value measurement on non-recurring basis | Level 3
Liabilities:
Mortgage loans recorded at fair value	$ 6		$ 7

[1] See Note 10, Investments and Cash.

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

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