Investments (Securities in a gross unrealized loss position by ratings) (Details) - USD ($) $ in Millions	Jun. 30, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	$ 29,612	$ 29,511
Gross Unrealized Losses	3,786	4,056
U.S. Government, Government agencies and Government-sponsored enterprises
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	2,479	2,355
Gross Unrealized Losses	334	337
AAA
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	1,662	1,559
Gross Unrealized Losses	283	298
AA
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	4,404	4,327
Gross Unrealized Losses	746	817
A
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	6,937	6,615
Gross Unrealized Losses	703	749
BBB
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	12,960	13,226
Gross Unrealized Losses	1,513	1,621
Non-investment grade
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	1,170	1,429
Gross Unrealized Losses	$ 207	$ 234