Investments (Securities in a gross unrealized loss position by ratings) (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	$ 20,691	$ 27,338
Gross Unrealized Losses	2,295	3,040
U.S. Government, Government agencies and Government-sponsored enterprises
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	1,959	2,567
Gross Unrealized Losses	281	373
AAA
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	1,367	1,830
Gross Unrealized Losses	248	283
AA
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	3,765	4,257
Gross Unrealized Losses	633	730
A
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	5,049	6,340
Gross Unrealized Losses	436	582
BBB
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	7,846	11,548
Gross Unrealized Losses	627	980
Non-investment grade
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	705	796
Gross Unrealized Losses	$ 70	$ 92