Fair Value Measurement - Financial Instruments Carried at Fair Value (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Assets:
Fixed-maturity securities	$ 10,733	$ 10,818
Other invested assets	60	55
Liabilities:
Credit derivative liabilities	224	209
Recurring [Member]
Assets:
Other invested assets	6	7
FG VIEs’ assets, at fair value	526	569
Other assets	166	139
Total assets carried at fair value	11,431	11,533
Liabilities:
Credit derivative liabilities	224	209
FG VIEs’ liabilities with recourse, at fair value	446	517
FG VIEs’ liabilities without recourse, at fair value	105	102
Total liabilities carried at fair value	775	828
Recurring [Member] | Level 1 [Member]
Assets:
Other invested assets	0	0
FG VIEs’ assets, at fair value	0	0
Other assets	32	25
Total assets carried at fair value	925	454
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	0	0
FG VIEs’ assets, at fair value	0	0
Other assets	42	38
Total assets carried at fair value	8,730	9,016
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	6	7
FG VIEs’ assets, at fair value	526	569
Other assets	92	76
Total assets carried at fair value	1,776	2,063
Liabilities:
Credit derivative liabilities	224	209
FG VIEs’ liabilities with recourse, at fair value	446	517
FG VIEs’ liabilities without recourse, at fair value	105	102
Total liabilities carried at fair value	775	828
Fixed Maturities [Member]
Assets:
Fixed-maturity securities	9,574	10,089
Fixed Maturities [Member] | Obligations of state and political subdivisions [Member]
Assets:
Fixed-maturity securities	4,683	4,911
Fixed Maturities [Member] | US government and agencies [Member]
Assets:
Fixed-maturity securities	165	175
Fixed Maturities [Member] | Corporate securities [Member]
Assets:
Fixed-maturity securities	2,267	2,136
Fixed Maturities [Member] | RMBS [Member]
Assets:
Fixed-maturity securities	938	982
Fixed Maturities [Member] | CMBS [Member]
Assets:
Fixed-maturity securities	495	539
Fixed Maturities [Member] | Asset-backed Securities [Member]
Assets:
Fixed-maturity securities	779	1,068
Fixed Maturities [Member] | Foreign government securities [Member]
Assets:
Fixed-maturity securities	247	278
Fixed Maturities [Member] | Recurring [Member]
Assets:
Fixed-maturity securities	9,574	10,089
Fixed Maturities [Member] | Recurring [Member] | Obligations of state and political subdivisions [Member]
Assets:
Fixed-maturity securities	4,683	4,911
Fixed Maturities [Member] | Recurring [Member] | US government and agencies [Member]
Assets:
Fixed-maturity securities	165	175
Fixed Maturities [Member] | Recurring [Member] | Corporate securities [Member]
Assets:
Fixed-maturity securities	2,267	2,136
Fixed Maturities [Member] | Recurring [Member] | RMBS [Member]
Assets:
Fixed-maturity securities	938	982
Fixed Maturities [Member] | Recurring [Member] | CMBS [Member]
Assets:
Fixed-maturity securities	495	539
Fixed Maturities [Member] | Recurring [Member] | Asset-backed Securities [Member]
Assets:
Fixed-maturity securities	779	1,068
Fixed Maturities [Member] | Recurring [Member] | Foreign government securities [Member]
Assets:
Fixed-maturity securities	247	278
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	8,422	8,678
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member] | Obligations of state and political subdivisions [Member]
Assets:
Fixed-maturity securities	4,578	4,812
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member] | US government and agencies [Member]
Assets:
Fixed-maturity securities	165	175
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member] | Corporate securities [Member]
Assets:
Fixed-maturity securities	2,219	2,080
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member] | RMBS [Member]
Assets:
Fixed-maturity securities	613	673
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member] | CMBS [Member]
Assets:
Fixed-maturity securities	495	539
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member] | Asset-backed Securities [Member]
Assets:
Fixed-maturity securities	105	121
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member] | Foreign government securities [Member]
Assets:
Fixed-maturity securities	247	278
Fixed Maturities [Member] | Recurring [Member] | Level 3 [Member]
Assets:
Fixed-maturity securities	1,152	1,411
Fixed Maturities [Member] | Recurring [Member] | Level 3 [Member] | Obligations of state and political subdivisions [Member]
Assets:
Fixed-maturity securities	105	99
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	48	56
Fixed Maturities [Member] | Recurring [Member] | Level 3 [Member] | RMBS [Member]
Assets:
Fixed-maturity securities	325	309
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	674	947
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	1,159	729
Short-term Investments [Member] | Recurring [Member]
Assets:
Fixed-maturity securities	1,159	729
Short-term Investments [Member] | Recurring [Member] | Level 1 [Member]
Assets:
Fixed-maturity securities	893	429
Short-term Investments [Member] | Recurring [Member] | Level 2 [Member]
Assets:
Fixed-maturity securities	266	300
Short-term Investments [Member] | Recurring [Member] | Level 3 [Member]
Assets:
Fixed-maturity securities	$ 0	$ 0