Fair Value Measurement - Financial Instruments Carried at Fair Value (Details) - USD ($) $ in Millions		Dec. 31, 2015	Dec. 31, 2014
Assets:
Fixed-maturity securities		$ 11,023	$ 11,258
Other invested assets		169	126
Other invested assets		93
Credit derivative assets		81	68
Liabilities:
Credit derivative liabilities		446	963
Investment funds measured using Net Asset Value excluded from fair value hierarchy		45	76
Recurring [Member]
Assets:
Other invested assets	[1]	12	24
Credit derivative assets		81	68
FG VIEs’ assets, at fair value		1,261	1,398	[2]
Other assets		106	78
Total assets carried at fair value		12,483	12,826
Liabilities:
Credit derivative liabilities		446	963
FG VIEs’ liabilities with recourse, at fair value		1,225	1,277
FG VIEs’ liabilities without recourse, at fair value		124	142
Total liabilities carried at fair value		1,795	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		0	0	[2]
Other assets		23	26
Total assets carried at fair value		328	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
Total liabilities carried at fair value		0	0
Recurring [Member] | Level 2 [Member]
Assets:
Other invested assets	[1]	5	17
Credit derivative assets		0	0
FG VIEs’ assets, at fair value		0	0	[2]
Other assets		21	17
Total assets carried at fair value		9,600	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
Total liabilities carried at fair value		0	0
Recurring [Member] | Level 3 [Member]
Assets:
Other invested assets	[1]	7	7
Credit derivative assets		81	68
FG VIEs’ assets, at fair value		1,261	1,398	[2]
Other assets		62	35
Total assets carried at fair value		2,555	2,278
Liabilities:
Credit derivative liabilities		446	963
FG VIEs’ liabilities with recourse, at fair value		1,225	1,277
FG VIEs’ liabilities without recourse, at fair value		124	142
Total liabilities carried at fair value		1,795	2,382
Fixed Maturities [Member]
Assets:
Fixed-maturity securities		10,627	10,491
Fixed Maturities [Member] | Obligations of state and political subdivisions [Member]
Assets:
Fixed-maturity securities		5,841	5,795
Fixed Maturities [Member] | US Treasury and Government [Member]
Assets:
Fixed-maturity securities		400	665
Fixed Maturities [Member] | Corporate securities [Member]
Assets:
Fixed-maturity securities		1,520	1,368
Fixed Maturities [Member] | Residential Mortgage-Backed Securities (RMBS) [Member]
Assets:
Fixed-maturity securities	[3]	1,245	1,285
Fixed Maturities [Member] | Commercial Mortgage Backed Securities (CMBS) [Member]
Assets:
Fixed-maturity securities	[3]	513	659
Fixed Maturities [Member] | Asset-backed Securities [Member]
Assets:
Fixed-maturity securities		825	417
Fixed Maturities [Member] | Foreign government securities [Member]
Assets:
Fixed-maturity securities		283	302
Fixed Maturities [Member] | Recurring [Member]
Assets:
Fixed-maturity securities		10,627	10,491
Fixed Maturities [Member] | Recurring [Member] | Obligations of state and political subdivisions [Member]
Assets:
Fixed-maturity securities		5,841	5,795
Fixed Maturities [Member] | Recurring [Member] | US Treasury and Government [Member]
Assets:
Fixed-maturity securities		400	665
Fixed Maturities [Member] | Recurring [Member] | Corporate securities [Member]
Assets:
Fixed-maturity securities		1,520	1,368
Fixed Maturities [Member] | Recurring [Member] | Residential Mortgage-Backed Securities (RMBS) [Member]
Assets:
Fixed-maturity securities		1,245	1,285
Fixed Maturities [Member] | Recurring [Member] | Commercial Mortgage Backed Securities (CMBS) [Member]
Assets:
Fixed-maturity securities		513	659
Fixed Maturities [Member] | Recurring [Member] | Asset-backed Securities [Member]
Assets:
Fixed-maturity securities		825	417
Fixed Maturities [Member] | Recurring [Member] | Foreign government securities [Member]
Assets:
Fixed-maturity securities		283	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] | Residential Mortgage-Backed Securities (RMBS) [Member]
Assets:
Fixed-maturity securities		0	0
Fixed Maturities [Member] | Recurring [Member] | Level 1 [Member] | Commercial Mortgage Backed Securities (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		9,543	9,721
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member] | Obligations of state and political subdivisions [Member]
Assets:
Fixed-maturity securities		5,833	5,757
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member] | US Treasury and Government [Member]
Assets:
Fixed-maturity securities		400	665
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member] | Corporate securities [Member]
Assets:
Fixed-maturity securities		1,449	1,289
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member] | Residential Mortgage-Backed Securities (RMBS) [Member]
Assets:
Fixed-maturity securities		897	860
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member] | Commercial Mortgage Backed Securities (CMBS) [Member]
Assets:
Fixed-maturity securities		513	659
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member] | Asset-backed Securities [Member]
Assets:
Fixed-maturity securities		168	189
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member] | Foreign government securities [Member]
Assets:
Fixed-maturity securities		283	302
Fixed Maturities [Member] | Recurring [Member] | Level 3 [Member]
Assets:
Fixed-maturity securities		1,084	770
Fixed Maturities [Member] | Recurring [Member] | Level 3 [Member] | Obligations of state and political subdivisions [Member]
Assets:
Fixed-maturity securities		8	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		71	79
Fixed Maturities [Member] | Recurring [Member] | Level 3 [Member] | Residential Mortgage-Backed Securities (RMBS) [Member]
Assets:
Fixed-maturity securities		348	425
Fixed Maturities [Member] | Recurring [Member] | Level 3 [Member] | Commercial Mortgage Backed Securities (CMBS) [Member]
Assets:
Fixed-maturity securities		0	0
Fixed Maturities [Member] | Recurring [Member] | Level 3 [Member] | Asset-backed Securities [Member]
Assets:
Fixed-maturity securities		657	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		396	767
Short-term Investments [Member] | Recurring [Member]
Assets:
Fixed-maturity securities		396	767
Short-term Investments [Member] | Recurring [Member] | Level 1 [Member]
Assets:
Fixed-maturity securities		305	359
Short-term Investments [Member] | Recurring [Member] | Level 2 [Member]
Assets:
Fixed-maturity securities		31	408
Short-term Investments [Member] | Recurring [Member] | Level 3 [Member]
Assets:
Fixed-maturity securities		$ 60	$ 0

[1] Excluded from the table above are investments funds of $45 million and $76 million as of December 31, 2015 and December 31, 2014, respectively, measured using NAV per share practical expedient. 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 54% of mortgage backed securities as of December 31, 2015 and 44% as of December 31, 2014 based on fair value.