Investments - Unrealized Losses on AFS Securities (Details) $ in Millions	Sep. 30, 2020 USD ($) security	Dec. 31, 2019 USD ($)
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 months	$ 10,900	$ 6,245
Fair Value, 12 months or greater	3,670	4,612
Total	14,570	10,857
Gross Unrealized Losses
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	527	195
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	337	254
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ 864	449
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Number of Positions \| security	353
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions \| security	1,748
Investments including related party
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 months	$ 13,200	6,964
Fair Value, 12 months or greater	3,902	4,854
Total	17,102	11,818
Gross Unrealized Losses
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	591	204
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	352	265
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	943	469
Related Party
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 months	2,300	719
Fair Value, 12 months or greater	232	242
Total	2,532	961
Gross Unrealized Losses
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	64	9
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	15	11
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ 79	20
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Number of Positions \| security	9
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions \| security	60
U.S. government and agencies
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 months	$ 9	3
Fair Value, 12 months or greater	0	0
Total	9	3
Gross Unrealized Losses
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	0	0
U.S. state, municipal and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 months	50	78
Fair Value, 12 months or greater	8	10
Total	58	88
Gross Unrealized Losses
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	1
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	1	0
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	1	1
Foreign governments
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 months	4
Fair Value, 12 months or greater	0
Total	4
Gross Unrealized Losses
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	0
Corporate
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 months	5,899	2,898
Fair Value, 12 months or greater	414	902
Total	6,313	3,800
Gross Unrealized Losses
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	248	140
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	57	70
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	305	210
CLO
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 months	2,475	1,959
Fair Value, 12 months or greater	3,118	3,241
Total	5,593	5,200
Gross Unrealized Losses
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	73	38
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	232	158
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	305	196
CLO \| Related Party
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 months	766	362
Fair Value, 12 months or greater	232	242
Total	998	604
Gross Unrealized Losses
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	15	7
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	15	11
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	30	18
ABS
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 months	1,238	642
Fair Value, 12 months or greater	82	255
Total	1,320	897
Gross Unrealized Losses
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	130	6
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	26	18
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	156	24
ABS \| Related Party
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 months	1,534	357
Fair Value, 12 months or greater	0	0
Total	1,534	357
Gross Unrealized Losses
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	49	2
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	49	2
CMBS
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 months	685	220
Fair Value, 12 months or greater	23	41
Total	708	261
Gross Unrealized Losses
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	60	4
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	20	4
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	80	8
RMBS
Debt Securities, Available-for-sale [Line Items]
Fair Value, Less than 12 months	540	445
Fair Value, 12 months or greater	25	163
Total	565	608
Gross Unrealized Losses
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	16	6
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	1	4
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ 17	$ 10

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