Fair Value Measurement - Financial Instruments Carried at Fair Value (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Assets:
Unrealized loss position	$ 9,501	$ 10,122
Other invested assets (includes $12 and $6 measured at fair value)	121	118
Assets of consolidated investment vehicles	645	572
Other assets	177	135
Liabilities:
Credit derivative liabilities	265	191
Liabilities of consolidated investment vehicles	431	482
Recurring [Member]
Assets:
Other invested assets (includes $12 and $6 measured at fair value)	12	6
FG VIEs’ assets, at fair value	368	442
Assets of consolidated investment vehicles	557	558
Other assets	177	135
Total assets carried at fair value	10,615	11,263
Liabilities:
Credit derivative liabilities	265	191
FG VIEs’ liabilities with recourse, at fair value	312	367
FG VIEs’ liabilities without recourse, at fair value	82	102
Liabilities of consolidated investment vehicles	426	481
Total liabilities carried at fair value	1,085	1,141
Recurring [Member] | Level 1 [Member]
Assets:
Other invested assets (includes $12 and $6 measured at fair value)	6	0
FG VIEs’ assets, at fair value	0	0
Assets of consolidated investment vehicles	0	0
Other assets	36	32
Total assets carried at fair value	907	1,093
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
Liabilities of consolidated investment vehicles	0	0
Total liabilities carried at fair value	0	0
Recurring [Member] | Level 2 [Member]
Assets:
Other invested assets (includes $12 and $6 measured at fair value)	0	0
FG VIEs’ assets, at fair value	0	0
Assets of consolidated investment vehicles	461	494
Other assets	38	45
Total assets carried at fair value	8,174	8,486
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
Liabilities of consolidated investment vehicles	0	0
Total liabilities carried at fair value	0	0
Recurring [Member] | Level 3 [Member]
Assets:
Other invested assets (includes $12 and $6 measured at fair value)	6	6
FG VIEs’ assets, at fair value	368	442
Assets of consolidated investment vehicles	96	64
Other assets	103	58
Total assets carried at fair value	1,534	1,684
Liabilities:
Credit derivative liabilities	265	191
FG VIEs’ liabilities with recourse, at fair value	312	367
FG VIEs’ liabilities without recourse, at fair value	82	102
Liabilities of consolidated investment vehicles	426	481
Total liabilities carried at fair value	1,085	1,141
Fixed Maturities [Member]
Assets:
Unrealized loss position	8,568	8,854
Fixed Maturities [Member] | Obligations of state and political subdivisions [Member]
Assets:
Unrealized loss position	4,204	4,340
Fixed Maturities [Member] | US government and agencies [Member]
Assets:
Unrealized loss position	175	147
Fixed Maturities [Member] | Corporate securities [Member]
Assets:
Unrealized loss position	2,233	2,221
Fixed Maturities [Member] | RMBS [Member]
Assets:
Unrealized loss position	717	775
Fixed Maturities [Member] | CMBS [Member]
Assets:
Unrealized loss position	414	419
Fixed Maturities [Member] | Asset-backed Securities [Member]
Assets:
Unrealized loss position	653	720
Fixed Maturities [Member] | Foreign government securities [Member]
Assets:
Unrealized loss position	172	232
Fixed Maturities [Member] | Recurring [Member]
Assets:
Unrealized loss position	8,568	8,854
Fixed Maturities [Member] | Recurring [Member] | Obligations of state and political subdivisions [Member]
Assets:
Unrealized loss position	4,204	4,340
Fixed Maturities [Member] | Recurring [Member] | US government and agencies [Member]
Assets:
Unrealized loss position	175	147
Fixed Maturities [Member] | Recurring [Member] | Corporate securities [Member]
Assets:
Unrealized loss position	2,233	2,221
Fixed Maturities [Member] | Recurring [Member] | RMBS [Member]
Assets:
Unrealized loss position	717	775
Fixed Maturities [Member] | Recurring [Member] | CMBS [Member]
Assets:
Unrealized loss position	414	419
Fixed Maturities [Member] | Recurring [Member] | Asset-backed Securities [Member]
Assets:
Unrealized loss position	653	720
Fixed Maturities [Member] | Recurring [Member] | Foreign government securities [Member]
Assets:
Unrealized loss position	172	232
Fixed Maturities [Member] | Recurring [Member] | Level 1 [Member]
Assets:
Unrealized loss position	0	0
Fixed Maturities [Member] | Recurring [Member] | Level 1 [Member] | Obligations of state and political subdivisions [Member]
Assets:
Unrealized loss position	0	0
Fixed Maturities [Member] | Recurring [Member] | Level 1 [Member] | US government and agencies [Member]
Assets:
Unrealized loss position	0	0
Fixed Maturities [Member] | Recurring [Member] | Level 1 [Member] | Corporate securities [Member]
Assets:
Unrealized loss position	0	0
Fixed Maturities [Member] | Recurring [Member] | Level 1 [Member] | RMBS [Member]
Assets:
Unrealized loss position	0	0
Fixed Maturities [Member] | Recurring [Member] | Level 1 [Member] | CMBS [Member]
Assets:
Unrealized loss position	0	0
Fixed Maturities [Member] | Recurring [Member] | Level 1 [Member] | Asset-backed Securities [Member]
Assets:
Unrealized loss position	0	0
Fixed Maturities [Member] | Recurring [Member] | Level 1 [Member] | Foreign government securities [Member]
Assets:
Unrealized loss position	0	0
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member]
Assets:
Unrealized loss position	7,607	7,740
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member] | Obligations of state and political subdivisions [Member]
Assets:
Unrealized loss position	4,118	4,233
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member] | US government and agencies [Member]
Assets:
Unrealized loss position	175	147
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member] | Corporate securities [Member]
Assets:
Unrealized loss position	2,207	2,180
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member] | RMBS [Member]
Assets:
Unrealized loss position	464	467
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member] | CMBS [Member]
Assets:
Unrealized loss position	414	419
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member] | Asset-backed Securities [Member]
Assets:
Unrealized loss position	57	62
Fixed Maturities [Member] | Recurring [Member] | Level 2 [Member] | Foreign government securities [Member]
Assets:
Unrealized loss position	172	232
Fixed Maturities [Member] | Recurring [Member] | Level 3 [Member]
Assets:
Unrealized loss position	961	1,114
Fixed Maturities [Member] | Recurring [Member] | Level 3 [Member] | Obligations of state and political subdivisions [Member]
Assets:
Unrealized loss position	86	107
Fixed Maturities [Member] | Recurring [Member] | Level 3 [Member] | US government and agencies [Member]
Assets:
Unrealized loss position	0	0
Fixed Maturities [Member] | Recurring [Member] | Level 3 [Member] | Corporate securities [Member]
Assets:
Unrealized loss position	26	41
Fixed Maturities [Member] | Recurring [Member] | Level 3 [Member] | RMBS [Member]
Assets:
Unrealized loss position	253	308
Fixed Maturities [Member] | Recurring [Member] | Level 3 [Member] | CMBS [Member]
Assets:
Unrealized loss position	0	0
Fixed Maturities [Member] | Recurring [Member] | Level 3 [Member] | Asset-backed Securities [Member]
Assets:
Unrealized loss position	596	658
Fixed Maturities [Member] | Recurring [Member] | Level 3 [Member] | Foreign government securities [Member]
Assets:
Unrealized loss position	0	0
Short-term Investments [Member]
Assets:
Unrealized loss position	933	1,268
Short-term Investments [Member] | Recurring [Member]
Assets:
Unrealized loss position	933	1,268
Short-term Investments [Member] | Recurring [Member] | Level 1 [Member]
Assets:
Unrealized loss position	865	1,061
Short-term Investments [Member] | Recurring [Member] | Level 2 [Member]
Assets:
Unrealized loss position	68	207
Short-term Investments [Member] | Recurring [Member] | Level 3 [Member]
Assets:
Unrealized loss position	$ 0	$ 0