Fair Value Measurement - Financial Instruments Carried at Fair Value (Details) - USD ($) $ in Millions		Jun. 30, 2015	Dec. 31, 2014
Assets:
Fixed-maturity securities		$ 11,416	$ 11,258
Other invested assets		215	126
Credit derivative assets		81	68
Liabilities:
Credit derivative liabilities		1,007	963
Recurring [Member]
Assets:
Other invested assets	[1]	90	100
Credit derivative assets		81	68
FG VIEs’ assets, at fair value	[2]	1,596	1,398
Other assets		107	78
Total assets carried at fair value		13,290	12,902
Liabilities:
Credit derivative liabilities		1,007	963
FG VIEs’ liabilities with recourse, at fair value		1,361	1,277
FG VIEs’ liabilities without recourse, at fair value		171	142
Other liabilities		17
Total liabilities carried at fair value		2,556	2,382
Recurring [Member] | Level 1 [Member]
Assets:
Other invested assets	[1]	0	0
Credit derivative assets		0	0
FG VIEs’ assets, at fair value	[2]	0	0
Other assets		25	26
Total assets carried at fair value		560	385
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
Other liabilities		0
Total liabilities carried at fair value		0	0
Recurring [Member] | Level 2 [Member]
Assets:
Other invested assets	[1]	7	17
Credit derivative assets		0	0
FG VIEs’ assets, at fair value	[2]	0	0
Other assets		22	17
Total assets carried at fair value		10,255	10,163
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
Other liabilities		0
Total liabilities carried at fair value		0	0
Recurring [Member] | Level 3 [Member]
Assets:
Other invested assets	[1]	83	83
Credit derivative assets		81	68
FG VIEs’ assets, at fair value	[2]	1,596	1,398
Other assets		60	35
Total assets carried at fair value		2,475	2,354
Liabilities:
Credit derivative liabilities		1,007	963
FG VIEs’ liabilities with recourse, at fair value		1,361	1,277
FG VIEs’ liabilities without recourse, at fair value		171	142
Other liabilities		17
Total liabilities carried at fair value		2,556	2,382
Fixed Maturities [Member]
Assets:
Fixed-maturity securities		10,582	10,491
Fixed Maturities [Member] | Obligations of state and political subdivisions [Member]
Assets:
Fixed-maturity securities		5,986	5,795
Fixed Maturities [Member] | US Treasury and Government [Member]
Assets:
Fixed-maturity securities		486	665
Fixed Maturities [Member] | Corporate securities [Member]
Assets:
Fixed-maturity securities		1,442	1,368
Fixed Maturities [Member] | RMBS [Member]
Assets:
Fixed-maturity securities	[3]	1,329	1,285
Fixed Maturities [Member] | CMBS [Member]
Assets:
Fixed-maturity securities	[3]	601	659
Fixed Maturities [Member] | Asset-backed Securities [Member]
Assets:
Fixed-maturity securities		431	417
Fixed Maturities [Member] | Foreign government securities [Member]
Assets:
Fixed-maturity securities		307	302
Fixed Maturities [Member] | Recurring [Member]
Assets:
Fixed-maturity securities		10,582	10,491
Fixed Maturities [Member] | Recurring [Member] | Obligations of state and political subdivisions [Member]
Assets:
Fixed-maturity securities		5,986	5,795
Fixed Maturities [Member] | Recurring [Member] | US Treasury and Government [Member]
Assets:
Fixed-maturity securities		486	665
Fixed Maturities [Member] | Recurring [Member] | Corporate securities [Member]
Assets:
Fixed-maturity securities		1,442	1,368
Fixed Maturities [Member] | Recurring [Member] | RMBS [Member]
Assets:
Fixed-maturity securities		1,329	1,285
Fixed Maturities [Member] | Recurring [Member] | CMBS [Member]
Assets:
Fixed-maturity securities		601	659
Fixed Maturities [Member] | Recurring [Member] | Asset-backed Securities [Member]
Assets:
Fixed-maturity securities		431	417
Fixed Maturities [Member] | Recurring [Member] | Foreign government securities [Member]
Assets:
Fixed-maturity securities		307	302
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		9,927	9,721
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member] | Obligations of state and political subdivisions [Member]
Assets:
Fixed-maturity securities		5,979	5,757
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member] | US Treasury and Government [Member]
Assets:
Fixed-maturity securities		486	665
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member] | Corporate securities [Member]
Assets:
Fixed-maturity securities		1,365	1,289
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member] | RMBS [Member]
Assets:
Fixed-maturity securities		994	860
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member] | CMBS [Member]
Assets:
Fixed-maturity securities		601	659
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member] | Asset-backed Securities [Member]
Assets:
Fixed-maturity securities		195	189
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member] | Foreign government securities [Member]
Assets:
Fixed-maturity securities		307	302
Fixed Maturities [Member] | Recurring [Member] | Level 3 [Member]
Assets:
Fixed-maturity securities		655	770
Fixed Maturities [Member] | Recurring [Member] | Level 3 [Member] | Obligations of state and political subdivisions [Member]
Assets:
Fixed-maturity securities		7	38
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		77	79
Fixed Maturities [Member] | Recurring [Member] | Level 3 [Member] | RMBS [Member]
Assets:
Fixed-maturity securities		335	425
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		236	228
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		834	767
Short-term Investments [Member] | Recurring [Member]
Assets:
Fixed-maturity securities		834	767
Short-term Investments [Member] | Recurring [Member] | Level 1 [Member]
Assets:
Fixed-maturity securities		535	359
Short-term Investments [Member] | Recurring [Member] | Level 2 [Member]
Assets:
Fixed-maturity securities		299	408
Short-term Investments [Member] | Recurring [Member] | Level 3 [Member]
Assets:
Fixed-maturity securities		$ 0	$ 0

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

[2] Excludes restricted cash.

[3] Government-agency obligations were approximately 53% of mortgage backed securities as of June 30, 2015 and 44% as of December 31, 2014 based on fair value.