Investments (Securities in a gross unrealized loss position by ratings) (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	$ 25,731	$ 29,511
Gross Unrealized Losses	2,995	4,056
U.S. Government, Government agencies and Government-sponsored enterprises
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	2,273	2,355
Gross Unrealized Losses	309	337
AAA
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	1,524	1,559
Gross Unrealized Losses	261	298
AA
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	3,817	4,327
Gross Unrealized Losses	658	817
A
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	5,652	6,615
Gross Unrealized Losses	517	749
BBB
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	11,523	13,226
Gross Unrealized Losses	1,095	1,621
Non-investment grade
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	942	1,429
Gross Unrealized Losses	$ 155	$ 234