Investments (Securities in a gross unrealized loss position by ratings) (Details) - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	$ 28,266	$ 29,511
Gross Unrealized Losses	3,418	4,056
U.S. Government, Government agencies and Government-sponsored enterprises
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	2,357	2,355
Gross Unrealized Losses	302	337
AAA
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	1,424	1,559
Gross Unrealized Losses	260	298
AA
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	4,053	4,327
Gross Unrealized Losses	670	817
A
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	6,440	6,615
Gross Unrealized Losses	619	749
BBB
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	12,651	13,226
Gross Unrealized Losses	1,360	1,621
Non-investment grade
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	1,341	1,429
Gross Unrealized Losses	$ 207	$ 234