Fair Value Measurement - Financial Instruments Carried at Fair Value (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Assets:
Fixed-maturity securities	$ 11,258		$ 10,615
Other invested assets	126		170
Credit derivative assets	68		94
Liabilities:
Credit derivative liabilities	963		1,787
Obligations of state and political subdivisions [Member]
Assets:
Fixed-maturity securities	4,949	[1]	4,554	[1]
Recurring [Member]
Assets:
Other invested assets	100	[2]	127	[2]
Credit derivative assets	68		94
FG VIEs’ assets, at fair value	1,398	[3]	2,565
Other assets	78		84
Total assets carried at fair value	12,902		13,485
Liabilities:
Credit derivative liabilities	963		1,787
FG VIEs’ liabilities with recourse, at fair value	1,277		1,790
FG VIEs’ liabilities without recourse, at fair value	142		1,081
Total liabilities carried at fair value	2,382		4,658
Recurring [Member] | Level 1 [Member]
Assets:
Other invested assets	0	[2]	0	[2]
Credit derivative assets	0		0
FG VIEs’ assets, at fair value	0	[3]	0
Other assets	26		27
Total assets carried at fair value	385		533
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
Recurring [Member] | Level 2 [Member]
Assets:
Other invested assets	17	[2]	119	[2]
Credit derivative assets	0		0
FG VIEs’ assets, at fair value	0	[3]	0
Other assets	17		11
Total assets carried at fair value	10,163		9,509
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
Recurring [Member] | Level 3 [Member]
Assets:
Other invested assets	83	[2]	8	[2]
Credit derivative assets	68		94
FG VIEs’ assets, at fair value	1,398	[3]	2,565
Other assets	35		46
Total assets carried at fair value	2,354		3,443
Liabilities:
Credit derivative liabilities	963		1,787
FG VIEs’ liabilities with recourse, at fair value	1,277		1,790
FG VIEs’ liabilities without recourse, at fair value	142		1,081
Total liabilities carried at fair value	2,382		4,658
Fixed Maturities [Member]
Assets:
Fixed-maturity securities	10,491		9,711
Fixed Maturities [Member] | Obligations of state and political subdivisions [Member]
Assets:
Fixed-maturity securities	5,795		5,079
Fixed Maturities [Member] | US Treasury and Government [Member]
Assets:
Fixed-maturity securities	665		700
Fixed Maturities [Member] | Corporate securities [Member]
Assets:
Fixed-maturity securities	1,368		1,340
Fixed Maturities [Member] | RMBS [Member]
Assets:
Fixed-maturity securities	1,285	[4]	1,122	[4]
Fixed Maturities [Member] | CMBS [Member]
Assets:
Fixed-maturity securities	659	[4]	549	[4]
Fixed Maturities [Member] | Asset-backed Securities [Member]
Assets:
Fixed-maturity securities	417		608
Fixed Maturities [Member] | Foreign government securities [Member]
Assets:
Fixed-maturity securities	302		313
Fixed Maturities [Member] | Recurring [Member]
Assets:
Fixed-maturity securities	10,491		9,711
Fixed Maturities [Member] | Recurring [Member] | Obligations of state and political subdivisions [Member]
Assets:
Fixed-maturity securities	5,795		5,079
Fixed Maturities [Member] | Recurring [Member] | US Treasury and Government [Member]
Assets:
Fixed-maturity securities	665		700
Fixed Maturities [Member] | Recurring [Member] | Corporate securities [Member]
Assets:
Fixed-maturity securities	1,368		1,340
Fixed Maturities [Member] | Recurring [Member] | RMBS [Member]
Assets:
Fixed-maturity securities	1,285		1,122
Fixed Maturities [Member] | Recurring [Member] | CMBS [Member]
Assets:
Fixed-maturity securities	659		549
Fixed Maturities [Member] | Recurring [Member] | Asset-backed Securities [Member]
Assets:
Fixed-maturity securities	417		608
Fixed Maturities [Member] | Recurring [Member] | Foreign government securities [Member]
Assets:
Fixed-maturity securities	302		313
Fixed Maturities [Member] | Recurring [Member] | Level 1 [Member]
Assets:
Fixed-maturity securities	0		0
Fixed Maturities [Member] | Recurring [Member] | Level 1 [Member] | Obligations of state and political subdivisions [Member]
Assets:
Fixed-maturity securities	0		0
Fixed Maturities [Member] | Recurring [Member] | Level 1 [Member] | US Treasury and Government [Member]
Assets:
Fixed-maturity securities	0		0
Fixed Maturities [Member] | Recurring [Member] | Level 1 [Member] | Corporate securities [Member]
Assets:
Fixed-maturity securities	0		0
Fixed Maturities [Member] | Recurring [Member] | Level 1 [Member] | RMBS [Member]
Assets:
Fixed-maturity securities	0		0
Fixed Maturities [Member] | Recurring [Member] | Level 1 [Member] | CMBS [Member]
Assets:
Fixed-maturity securities	0		0
Fixed Maturities [Member] | Recurring [Member] | Level 1 [Member] | Asset-backed Securities [Member]
Assets:
Fixed-maturity securities	0		0
Fixed Maturities [Member] | Recurring [Member] | Level 1 [Member] | Foreign government securities [Member]
Assets:
Fixed-maturity securities	0		0
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member]
Assets:
Fixed-maturity securities	9,721		8,981
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member] | Obligations of state and political subdivisions [Member]
Assets:
Fixed-maturity securities	5,757		5,043
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member] | US Treasury and Government [Member]
Assets:
Fixed-maturity securities	665		700
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member] | Corporate securities [Member]
Assets:
Fixed-maturity securities	1,289		1,204
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member] | RMBS [Member]
Assets:
Fixed-maturity securities	860		832
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member] | CMBS [Member]
Assets:
Fixed-maturity securities	659		549
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member] | Asset-backed Securities [Member]
Assets:
Fixed-maturity securities	189		340
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member] | Foreign government securities [Member]
Assets:
Fixed-maturity securities	302		313
Fixed Maturities [Member] | Recurring [Member] | Level 3 [Member]
Assets:
Fixed-maturity securities	770		730
Fixed Maturities [Member] | Recurring [Member] | Level 3 [Member] | Obligations of state and political subdivisions [Member]
Assets:
Fixed-maturity securities	38		36
Fixed Maturities [Member] | Recurring [Member] | Level 3 [Member] | US Treasury and Government [Member]
Assets:
Fixed-maturity securities	0		0
Fixed Maturities [Member] | Recurring [Member] | Level 3 [Member] | Corporate securities [Member]
Assets:
Fixed-maturity securities	79		136
Fixed Maturities [Member] | Recurring [Member] | Level 3 [Member] | RMBS [Member]
Assets:
Fixed-maturity securities	425		290
Fixed Maturities [Member] | Recurring [Member] | Level 3 [Member] | CMBS [Member]
Assets:
Fixed-maturity securities	0		0
Fixed Maturities [Member] | Recurring [Member] | Level 3 [Member] | Asset-backed Securities [Member]
Assets:
Fixed-maturity securities	228		268
Fixed Maturities [Member] | Recurring [Member] | Level 3 [Member] | Foreign government securities [Member]
Assets:
Fixed-maturity securities	0		0
Short-term Investments [Member]
Assets:
Fixed-maturity securities	767		904
Short-term Investments [Member] | Recurring [Member]
Assets:
Fixed-maturity securities	767		904
Short-term Investments [Member] | Recurring [Member] | Level 1 [Member]
Assets:
Fixed-maturity securities	359		506
Short-term Investments [Member] | Recurring [Member] | Level 2 [Member]
Assets:
Fixed-maturity securities	408		398
Short-term Investments [Member] | Recurring [Member] | Level 3 [Member]
Assets:
Fixed-maturity securities	$ 0		$ 0

[1] Excludes $846 million and $525 million as of December 31, 2014 and 2013, respectively, of pre-refunded bonds, at fair value. The credit ratings are based on the underlying ratings and do not include any benefit from bond insurance.

[2] Includes Level 3 mortgage loans that are recorded at fair value on a non-recurring basis.

[3] Exclude restricted cash.

[4] Government-agency obligations were approximately 44% of mortgage backed securities as of December 31, 2014 and 50% as of December 31, 2013 based on fair value.