Investments - Investments - Unrealized Losses on AFS Securities (Details) $ in Millions	Mar. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions	4,002
Percentage of Gross Unrealized Losses Depressed Less than Twenty Percent of Cost or Amortized Cost	95.00%
ABS
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 982	$ 604
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	7	6
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	942	1,043
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	36	39
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	1,924	1,647
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	43	45
Collateralized Loan Obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	1,107	209
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	4	1
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	295	2,249
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	1	16
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	1,402	2,458
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	5	17
CMBS
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	59	117
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1	7
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	2,794	2,837
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	302	341
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	2,853	2,954
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	303	348
Corporate
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	1,733	810
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	25	10
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	11,000	11,149
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	1,054	1,003
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	12,733	11,959
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	1,079	1,013
Foreign Govt./Govt. Agencies
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	96	27
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	344	368
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	29	27
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	440	395
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	30	27
Municipal
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	664	329
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	6	3
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	3,212	3,196
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	329	296
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	3,876	3,525
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	335	299
RMBS
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	685	181
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	8	3
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	3,061	3,207
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	418	403
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	3,746	3,388
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	426	406
U.S. Treasuries
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	287	120
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	14	11
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	999	1,121
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	164	139
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	1,286	1,241
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	178	150
Available-for-sale Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	5,613	2,397
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	66	41
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	22,647	25,170
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	2,333	2,264
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	28,260	27,567
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	$ 2,399	$ 2,305