Fair Value Measurement - Financial Instruments Carried at Fair Value (Details) - USD ($) $ in Millions		Jun. 30, 2016	Dec. 31, 2015
Assets:
Fixed-maturity securities		$ 10,545	$ 11,023
Other invested assets		170	169
Credit derivative assets		36	81
Liabilities:
Credit derivative liabilities		432	446
Investment funds, fair value		46	45
Recurring [Member]
Assets:
Other invested assets	[1]	13	12
Credit derivative assets		36	81
FG VIEs’ assets, at fair value		814	1,261
Other assets		84	106
Total assets carried at fair value		11,492	12,483
Liabilities:
Credit derivative liabilities		432	446
FG VIEs’ liabilities with recourse, at fair value		790	1,225
FG VIEs’ liabilities without recourse, at fair value		115	124
Total liabilities carried at fair value		1,337	1,795
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
Other assets		22	23
Total assets carried at fair value		543	328
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]	6	5
Credit derivative assets		0	0
FG VIEs’ assets, at fair value		0	0
Other assets		27	21
Total assets carried at fair value		9,045	9,600
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		36	81
FG VIEs’ assets, at fair value		814	1,261
Other assets		35	62
Total assets carried at fair value		1,904	2,555
Liabilities:
Credit derivative liabilities		432	446
FG VIEs’ liabilities with recourse, at fair value		790	1,225
FG VIEs’ liabilities without recourse, at fair value		115	124
Total liabilities carried at fair value		1,337	1,795
Fixed Maturities [Member]
Assets:
Fixed-maturity securities		9,960	10,627
Fixed Maturities [Member] | Obligations of state and political subdivisions [Member]
Assets:
Fixed-maturity securities		5,603	5,841
Fixed Maturities [Member] | US government and agencies [Member]
Assets:
Fixed-maturity securities		326	400
Fixed Maturities [Member] | Corporate securities [Member]
Assets:
Fixed-maturity securities		1,443	1,520
Fixed Maturities [Member] | RMBS [Member]
Assets:
Fixed-maturity securities	[2]	1,062	1,245
Fixed Maturities [Member] | CMBS [Member]
Assets:
Fixed-maturity securities	[2]	539	513
Fixed Maturities [Member] | Asset-backed Securities [Member]
Assets:
Fixed-maturity securities		730	825
Fixed Maturities [Member] | Foreign government securities [Member]
Assets:
Fixed-maturity securities		257	283
Fixed Maturities [Member] | Recurring [Member]
Assets:
Fixed-maturity securities		9,960	10,627
Fixed Maturities [Member] | Recurring [Member] | Obligations of state and political subdivisions [Member]
Assets:
Fixed-maturity securities		5,603	5,841
Fixed Maturities [Member] | Recurring [Member] | US government and agencies [Member]
Assets:
Fixed-maturity securities		326	400
Fixed Maturities [Member] | Recurring [Member] | Corporate securities [Member]
Assets:
Fixed-maturity securities		1,443	1,520
Fixed Maturities [Member] | Recurring [Member] | RMBS [Member]
Assets:
Fixed-maturity securities		1,062	1,245
Fixed Maturities [Member] | Recurring [Member] | CMBS [Member]
Assets:
Fixed-maturity securities		539	513
Fixed Maturities [Member] | Recurring [Member] | Asset-backed Securities [Member]
Assets:
Fixed-maturity securities		730	825
Fixed Maturities [Member] | Recurring [Member] | Foreign government securities [Member]
Assets:
Fixed-maturity securities		257	283
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 government and agencies [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		8,948	9,543
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member] | Obligations of state and political subdivisions [Member]
Assets:
Fixed-maturity securities		5,562	5,833
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member] | US government and agencies [Member]
Assets:
Fixed-maturity securities		326	400
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member] | Corporate securities [Member]
Assets:
Fixed-maturity securities		1,385	1,449
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member] | RMBS [Member]
Assets:
Fixed-maturity securities		713	897
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member] | CMBS [Member]
Assets:
Fixed-maturity securities		539	513
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member] | Asset-backed Securities [Member]
Assets:
Fixed-maturity securities		166	168
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member] | Foreign government securities [Member]
Assets:
Fixed-maturity securities		257	283
Fixed Maturities [Member] | Recurring [Member] | Level 3 [Member]
Assets:
Fixed-maturity securities		1,012	1,084
Fixed Maturities [Member] | Recurring [Member] | Level 3 [Member] | Obligations of state and political subdivisions [Member]
Assets:
Fixed-maturity securities		41	8
Fixed Maturities [Member] | Recurring [Member] | Level 3 [Member] | US government and agencies [Member]
Assets:
Fixed-maturity securities		0	0
Fixed Maturities [Member] | Recurring [Member] | Level 3 [Member] | Corporate securities [Member]
Assets:
Fixed-maturity securities		58	71
Fixed Maturities [Member] | Recurring [Member] | Level 3 [Member] | RMBS [Member]
Assets:
Fixed-maturity securities		349	348
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		564	657
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		585	396
Short-term Investments [Member] | Recurring [Member]
Assets:
Fixed-maturity securities		585	396
Short-term Investments [Member] | Recurring [Member] | Level 1 [Member]
Assets:
Fixed-maturity securities		521	305
Short-term Investments [Member] | Recurring [Member] | Level 2 [Member]
Assets:
Fixed-maturity securities		64	31
Short-term Investments [Member] | Recurring [Member] | Level 3 [Member]
Assets:
Fixed-maturity securities		$ 0	$ 60

[1] Excluded from the table above are investments funds of $46 million and $45 million as of June 30, 2016 and December 31, 2015, respectively, measured using NAV per share. Includes Level 3 mortgage loans that are recorded at fair value on a non-recurring basis.

[2] Government-agency obligations were approximately 47% of mortgage backed securities as of June 30, 2016 and 54% as of December 31, 2015 based on fair value.