Fair Value Measurements - Fair Value Recurring Basis, Unobservable Input (Details) - Fair Value, Measurements, Recurring - Significant Unobservable Inputs (Level 3) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Assets
Beginning balance	$ 1,402	$ 1,508	$ 1,502	$ 1,646
Total realized/unrealized gains (losses), Included in net income	(25)	(4)	(42)	(8)
Total realized/unrealized gains (losses), Included in OCI	78	2	(34)	8
Purchases	88	383	220	504
Settlements	(78)	(73)	(168)	(131)
Sales	(19)	(44)	(34)	(118)
Transfers into Level 3	412	34	459	46
Transfers out of Level 3	(48)	(82)	(93)	(223)
Ending balance	1,810	1,724	1,810	1,724
Liabilities
Changes in Unrealized Gain/(Loss) Included in Net Income, Liabilities	0	(2)	12	(6)
Freestanding Derivatives, net
Beginning balance		(1)		(4)
Realized/unrealized gain/loss included in net income, liabilities		(4)		(7)
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		3		3
Contingent Consideration
Liabilities
Beginning balance	0	(29)	(22)	(35)
Changes in Unrealized Gain/(Loss) Included in Net Income, Liabilities	0	(2)	12	(6)
Total realized/unrealized gains (losses), Included in OCI	0	0	0	0
Purchases	0	0	0	0
Settlements	0	10	(10)	20
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Sales	0	0	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Ending balance	0	(21)	0	(21)
Liability [Member]
Liabilities
Beginning balance	0	(29)	(37)	(35)
Changes in Unrealized Gain/(Loss) Included in Net Income, Liabilities	0	(2)	48	(6)
Total realized/unrealized gains (losses), Included in OCI	0	0	0	0
Purchases	0	0	0	0
Settlements	0	10	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	(21)	0	(21)
Equity
Freestanding Derivatives, net
Beginning balance		(1)		(3)
Realized/unrealized gain/loss included in net income, liabilities		(4)		(6)
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	3	0	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
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
Derivative [Member] | 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
Ending balance	0		0
Equity Securities, at fair value
Assets
Beginning balance	69
Total realized/unrealized gains (losses), Included in net income	(3)
Total realized/unrealized gains (losses), Included in OCI	0
Purchases	0
Settlements	0
Sales	0
Transfers into Level 3	0
Transfers out of Level 3	0
Ending balance	66		66
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
Securities available-for-sale and other | Total fixed maturities, FVO
Assets
Beginning balance	1,319	1,434	1,414	1,565
Total realized/unrealized gains (losses), Included in net income	(22)	0	(32)	0
Total realized/unrealized gains (losses), Included in OCI	78	2	(34)	8
Purchases	88	379	217	495
Settlements	(78)	(73)	(167)	(131)
Sales	(19)	(39)	(34)	(105)
Transfers into Level 3	412	34	459	46
Transfers out of Level 3	(48)	(82)	(93)	(223)
Ending balance	1,730	1,655	1,730	1,655
Securities available-for-sale and other | ABS | Total fixed maturities, FVO
Assets
Beginning balance	19	9	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	23	5	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	(19)	(9)	(34)	(9)
Ending balance	23	5	23	5
Securities available-for-sale and other | CLOs | Total fixed maturities, FVO
Assets
Beginning balance	83	114	95	100
Total realized/unrealized gains (losses), Included in net income	0	0	0	0
Total realized/unrealized gains (losses), Included in OCI	4	0	(2)	0
Purchases	19	202	19	237
Settlements	(7)	(10)	(13)	(10)
Sales	0	0	0	(6)
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	(20)	0	(35)
Ending balance	99	286	99	286
Securities available-for-sale and other | CMBS | Total fixed maturities, FVO
Assets
Beginning balance	18	12	9	12
Total realized/unrealized gains (losses), Included in net income	0	0	0	0
Total realized/unrealized gains (losses), Included in OCI	0	0	0	1
Purchases	3	24	13	24
Settlements	(1)	(1)	(2)	(2)
Sales	0	0	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Ending balance	20	35	20	35
Securities available-for-sale and other | Corporate | Total fixed maturities, FVO
Assets
Beginning balance	709	525	732	520
Total realized/unrealized gains (losses), Included in net income	(22)	0	(32)	(1)
Total realized/unrealized gains (losses), Included in OCI	61	2	(19)	9
Purchases	22	58	116	95
Settlements	(28)	(4)	(64)	(6)
Sales	(19)	(39)	(27)	(64)
Transfers into Level 3	412	34	459	46
Transfers out of Level 3	(26)	(8)	(56)	(31)
Ending balance	1,109	568	1,109	568
Securities available-for-sale and other | Foreign government/government agencies | Total fixed maturities, FVO
Assets
Beginning balance	3	3	3	3
Total realized/unrealized gains (losses), Included in net income	0	0	0	0
Total realized/unrealized gains (losses), Included in OCI	0	0	0	0
Purchases	0	0	0	0
Settlements	0	0	0	0
Sales	0	0	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	(3)	0	(3)	0
Ending balance	0	3	0	3
Securities available-for-sale and other | RMBS | Total fixed maturities, FVO
Assets
Beginning balance	487	771	560	920
Total realized/unrealized gains (losses), Included in net income	0	0	0	1
Total realized/unrealized gains (losses), Included in OCI	13	0	(12)	(2)
Purchases	21	90	26	134
Settlements	(42)	(58)	(88)	(112)
Sales	0	0	(7)	(35)
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	(45)	0	(148)
Ending balance	479	758	479	758
Equity Securities, at fair value
Assets
Beginning balance		73		77
Total realized/unrealized gains (losses), Included in net income		0		(1)
Total realized/unrealized gains (losses), Included in OCI		0		0
Purchases		4		9
Settlements		0		0
Sales		(5)		(13)
Transfers into Level 3		0		0
Transfers out of Level 3		0		0
Ending balance		$ 72		$ 72
Equity Securities, at fair value | 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			3
Settlements			0
Sales			0
Transfers into Level 3			0
Transfers out of Level 3			0
Ending balance	$ 66		$ 66