Fair Value Measurement - Financial Instruments Carried at Fair Value (Details) - USD ($) $ in Millions		Sep. 30, 2016	Dec. 31, 2015
Assets:
Fixed-maturity securities		$ 11,280	$ 11,023
Other invested assets		165	169
Credit derivative assets		28	81
Liabilities:
Credit derivative liabilities		509	446
Investment funds, fair value		48	45
Recurring [Member]
Assets:
Other invested assets	[1]	12	12
Credit derivative assets		28	81
FG VIEs’ assets, at fair value		877	1,261
Other assets		62	106
Total assets carried at fair value		12,259	12,483
Liabilities:
Credit derivative liabilities		509	446
FG VIEs’ liabilities with recourse, at fair value		832	1,225
FG VIEs’ liabilities without recourse, at fair value		153	124
Total liabilities carried at fair value		1,494	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		23	23
Total assets carried at fair value		392	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]	4	5
Credit derivative assets		0	0
FG VIEs’ assets, at fair value		0	0
Other assets		27	21
Total assets carried at fair value		9,767	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]	8	7
Credit derivative assets		28	81
FG VIEs’ assets, at fair value		877	1,261
Other assets		12	62
Total assets carried at fair value		2,100	2,555
Liabilities:
Credit derivative liabilities		509	446
FG VIEs’ liabilities with recourse, at fair value		832	1,225
FG VIEs’ liabilities without recourse, at fair value		153	124
Total liabilities carried at fair value		1,494	1,795
Fixed Maturities [Member]
Assets:
Fixed-maturity securities		10,752	10,627
Fixed Maturities [Member] | Obligations of state and political subdivisions [Member]
Assets:
Fixed-maturity securities		5,669	5,841
Fixed Maturities [Member] | US government and agencies [Member]
Assets:
Fixed-maturity securities		405	400
Fixed Maturities [Member] | Corporate securities [Member]
Assets:
Fixed-maturity securities		1,775	1,520
Fixed Maturities [Member] | RMBS [Member]
Assets:
Fixed-maturity securities	[2]	1,105	1,245
Fixed Maturities [Member] | CMBS [Member]
Assets:
Fixed-maturity securities	[2]	649	513
Fixed Maturities [Member] | Asset-backed Securities [Member]
Assets:
Fixed-maturity securities		892	825
Fixed Maturities [Member] | Foreign government securities [Member]
Assets:
Fixed-maturity securities		257	283
Fixed Maturities [Member] | Recurring [Member]
Assets:
Fixed-maturity securities		10,752	10,627
Fixed Maturities [Member] | Recurring [Member] | Obligations of state and political subdivisions [Member]
Assets:
Fixed-maturity securities		5,669	5,841
Fixed Maturities [Member] | Recurring [Member] | US government and agencies [Member]
Assets:
Fixed-maturity securities		405	400
Fixed Maturities [Member] | Recurring [Member] | Corporate securities [Member]
Assets:
Fixed-maturity securities		1,775	1,520
Fixed Maturities [Member] | Recurring [Member] | RMBS [Member]
Assets:
Fixed-maturity securities		1,105	1,245
Fixed Maturities [Member] | Recurring [Member] | CMBS [Member]
Assets:
Fixed-maturity securities		649	513
Fixed Maturities [Member] | Recurring [Member] | Asset-backed Securities [Member]
Assets:
Fixed-maturity securities		892	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		9,577	9,543
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member] | Obligations of state and political subdivisions [Member]
Assets:
Fixed-maturity securities		5,626	5,833
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member] | US government and agencies [Member]
Assets:
Fixed-maturity securities		405	400
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member] | Corporate securities [Member]
Assets:
Fixed-maturity securities		1,717	1,449
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member] | RMBS [Member]
Assets:
Fixed-maturity securities		722	897
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member] | CMBS [Member]
Assets:
Fixed-maturity securities		649	513
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member] | Asset-backed Securities [Member]
Assets:
Fixed-maturity securities		201	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		1,175	1,084
Fixed Maturities [Member] | Recurring [Member] | Level 3 [Member] | Obligations of state and political subdivisions [Member]
Assets:
Fixed-maturity securities		43	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		383	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		691	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		528	396
Short-term Investments [Member] | Recurring [Member]
Assets:
Fixed-maturity securities		528	396
Short-term Investments [Member] | Recurring [Member] | Level 1 [Member]
Assets:
Fixed-maturity securities		369	305
Short-term Investments [Member] | Recurring [Member] | Level 2 [Member]
Assets:
Fixed-maturity securities		159	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 $48 million and $45 million as of September 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 44% of mortgage backed securities as of September 30, 2016 and 54% as of December 31, 2015 based on fair value.