Fair Value Measurements - Fair Value Recurring Basis, Unobservable Input (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Freestanding Derivatives, net
Realized/unrealized gain/loss included in OCI, liabilities		$ 0
Purchases		0
Sales		0
Transfers into level 3		0
Transfers out of level 3		0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Assets
Beginning balance	$ 1,810	1,727	$ 1,502	$ 1,643
Total realized/unrealized gains (losses), Included in net income	(2)	(5)	(44)	(7)
Total realized/unrealized gains (losses), Included in OCI	26	(3)	(8)	5
Purchases	217	268	437	772
Settlements	(114)	(67)	(282)	(198)
Sales	0	(4)	(34)	(122)
Transfers into Level 3	34	15	493	61
Transfers out of Level 3	(202)	(205)	(295)	(428)
Ending balance	1,769	1,726	1,769	1,726
Liabilities
Changes in Unrealized Gain/(Loss) Included in Net Income, Liabilities	0	(2)	12	(14)
Freestanding Derivatives, net
Beginning balance		3
Realized/unrealized gain/loss included in net income, liabilities		(2)
Settlements		0
Ending balance		5		5
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Other investments
Freestanding Derivatives, net
Beginning balance				(1)
Realized/unrealized gain/loss included in net income, liabilities				(1)
Realized/unrealized gain/loss included in OCI, liabilities				0
Purchases				0
Settlements				0
Sales				0
Transfers into level 3				0
Transfers out of level 3				0
Ending balance		0		0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Other liabilities
Freestanding Derivatives, net
Beginning balance				(3)
Realized/unrealized gain/loss included in net income, liabilities				(8)
Realized/unrealized gain/loss included in OCI, liabilities				0
Purchases				0
Settlements				0
Sales				0
Transfers into level 3				0
Transfers out of level 3				0
Ending balance		5		5
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Contingent Consideration
Liabilities
Beginning balance		(21)	(22)	(35)
Changes in Unrealized Gain/(Loss) Included in Net Income, Liabilities	0	0	12	(6)
Total realized/unrealized gains (losses), Included in OCI		0	0	0
Purchases		0	0	0
Settlements		0	10	20
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Sales		0	0	0
Transfers into Level 3		0	0	0
Transfers out of Level 3		0	0	0
Ending balance	0	(21)	0	(21)
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Liability [Member]
Liabilities
Beginning balance	0	(24)	(37)	(32)
Changes in Unrealized Gain/(Loss) Included in Net Income, Liabilities	0	(2)	48	(14)
Total realized/unrealized gains (losses), Included in OCI	0	0	0	0
Purchases	0	0	0	0
Settlements	0	0	10	20
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Sales	0	0	(21)	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Ending balance	0	(26)	0	(26)
Freestanding Derivatives, net
Beginning balance			15
Realized/unrealized gain/loss included in net income, liabilities			36
Realized/unrealized gain/loss included in OCI, liabilities			0
Purchases			0
Settlements			0
Sales			(21)
Transfers into level 3			0
Transfers out of level 3			0
Ending balance	0		0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Equity
Freestanding Derivatives, net
Beginning balance		3		(3)
Realized/unrealized gain/loss included in net income, liabilities		(2)		(8)
Realized/unrealized gain/loss included in OCI, liabilities		0		0
Purchases		0		0
Settlements		0		0
Sales		0		0
Transfers into level 3		0		0
Transfers out of level 3		0		0
Ending balance	0	5	0	5
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Equity | Liability [Member]
Freestanding Derivatives, net
Beginning balance			15
Realized/unrealized gain/loss included in net income, liabilities			36
Realized/unrealized gain/loss included in OCI, liabilities			0
Purchases			0
Settlements			0
Sales			(21)
Transfers into level 3			0
Transfers out of level 3			0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Interest rate derivatives
Freestanding Derivatives, net
Beginning balance				(1)
Realized/unrealized gain/loss included in net income, liabilities				(1)
Realized/unrealized gain/loss included in OCI, liabilities				0
Purchases				0
Settlements				0
Sales				0
Transfers into level 3				0
Transfers out of level 3				0
Ending balance		0		0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Equity Securities, at fair value
Assets
Beginning balance	66
Total realized/unrealized gains (losses), Included in net income	0
Total realized/unrealized gains (losses), Included in OCI	0
Purchases	3
Settlements	0
Sales	0
Transfers into Level 3	0
Transfers out of Level 3	0
Ending balance	69		69
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Short-term investments
Assets
Beginning balance	14		15
Total realized/unrealized gains (losses), Included in net income	0		0
Total realized/unrealized gains (losses), Included in OCI	0		0
Purchases	0		0
Settlements	0		(1)
Sales	0		0
Transfers into Level 3	0		0
Transfers out of Level 3	0		0
Ending balance	14		14
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Securities available-for-sale and other | Total fixed maturities, FVO
Assets
Beginning balance	1,730	1,655	1,414	1,565
Total realized/unrealized gains (losses), Included in net income	(2)	(3)	(34)	(3)
Total realized/unrealized gains (losses), Included in OCI	26	(3)	(8)	5
Purchases	214	268	431	763
Settlements	(114)	(67)	(281)	(198)
Sales	0	(4)	(34)	(109)
Transfers into Level 3	34	15	493	61
Transfers out of Level 3	(202)	(205)	(295)	(428)
Ending balance	1,686	1,656	1,686	1,656
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Securities available-for-sale and other | ABS | Total fixed maturities, FVO
Assets
Beginning balance	23	5	15	10
Total realized/unrealized gains (losses), Included in net income	0	0	0	0
Total realized/unrealized gains (losses), Included in OCI	0	0	(1)	0
Purchases	0	0	43	5
Settlements	0	0	0	(1)
Sales	0	0	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	(23)	(5)	(57)	(14)
Ending balance	0	0	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Securities available-for-sale and other | CLOs | Total fixed maturities, FVO
Assets
Beginning balance	99	286	95	100
Total realized/unrealized gains (losses), Included in net income	0	0	0	0
Total realized/unrealized gains (losses), Included in OCI	1	0	(1)	0
Purchases	63	92	82	329
Settlements	(3)	(8)	(16)	(18)
Sales	0	0	0	(6)
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	(19)	(74)	(19)	(109)
Ending balance	141	296	141	296
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Securities available-for-sale and other | CMBS | Total fixed maturities, FVO
Assets
Beginning balance	20	35	9	12
Total realized/unrealized gains (losses), Included in net income	0	0	0	0
Total realized/unrealized gains (losses), Included in OCI	2	0	2	1
Purchases	66	10	79	34
Settlements	(1)	(1)	(3)	(3)
Sales	0	0	0	0
Transfers into Level 3	5	0	5	0
Transfers out of Level 3	0	(24)	0	(24)
Ending balance	92	20	92	20
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Securities available-for-sale and other | Corporate | Total fixed maturities, FVO
Assets
Beginning balance	1,109	568	732	520
Total realized/unrealized gains (losses), Included in net income	1	(3)	(31)	(4)
Total realized/unrealized gains (losses), Included in OCI	19	0	0	9
Purchases	45	166	161	261
Settlements	(62)	(7)	(126)	(13)
Sales	0	(4)	(27)	(68)
Transfers into Level 3	22	15	481	61
Transfers out of Level 3	(138)	(12)	(194)	(43)
Ending balance	996	723	996	723
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Securities available-for-sale and other | Foreign government/government agencies | Total fixed maturities, FVO
Assets
Beginning balance		3	3	3
Total realized/unrealized gains (losses), Included in net income		0	0	0
Total realized/unrealized gains (losses), Included in OCI		0	0	0
Purchases		0	0	0
Settlements		0	0	0
Sales		0	0	0
Transfers into Level 3		0	0	0
Transfers out of Level 3		0	(3)	0
Ending balance	0	3	0	3
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Securities available-for-sale and other | RMBS | Total fixed maturities, FVO
Assets
Beginning balance	479	758	560	920
Total realized/unrealized gains (losses), Included in net income	0	0	0	1
Total realized/unrealized gains (losses), Included in OCI	2	(3)	(10)	(5)
Purchases	40	0	66	134
Settlements	(48)	(51)	(136)	(163)
Sales	0	0	(7)	(35)
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	(22)	(90)	(22)	(238)
Ending balance	451	614	451	614
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Securities available-for-sale and other | Municipal | Total fixed maturities, FVO
Assets
Beginning balance	0		0
Total realized/unrealized gains (losses), Included in net income	(3)		(3)
Total realized/unrealized gains (losses), Included in OCI	2		2
Purchases	0		0
Settlements	0		0
Sales	0		0
Transfers into Level 3	7		7
Transfers out of Level 3	0		0
Ending balance	6		6
Equity Securities, at fair value | Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Assets
Beginning balance		72		77
Total realized/unrealized gains (losses), Included in net income		(2)		(3)
Total realized/unrealized gains (losses), Included in OCI		0		0
Purchases		0		9
Settlements		0		0
Sales		0		(13)
Transfers into Level 3		0		0
Transfers out of Level 3		0		0
Ending balance		$ 70		$ 70
Equity Securities, at fair value | Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Equity Securities, at fair value
Assets
Beginning balance			73
Total realized/unrealized gains (losses), Included in net income			(10)
Total realized/unrealized gains (losses), Included in OCI			0
Purchases			6
Settlements			0
Sales			0
Transfers into Level 3			0
Transfers out of Level 3			0
Ending balance	$ 69		$ 69