Temporarily Impaired Available for Sale Debt Securities by Time Period Impaired (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	$ 2,504	$ 3,856
Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	31	201
Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	7,768	4,642
Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	803	633
Unrealized Loss Position, Fair Value	10,272	8,498
Unrealized Loss Position, Accumulated Loss	834	834
Taxable bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	2,442	3,705
Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	29	199
Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	7,648	4,627
Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	800	631
Unrealized Loss Position, Fair Value	10,090	8,332
Unrealized Loss Position, Accumulated Loss	829	830
Restricted investments [Member]
Debt Securities, Available-for-sale [Line Items]
Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	62	151
Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	2	2
Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	120	15
Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	3	2
Unrealized Loss Position, Fair Value	182	166
Unrealized Loss Position, Accumulated Loss	$ 5	$ 4