Investments (Securities in a gross unrealized loss position by ratings) (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	$ 16,524	$ 6,065
Gross Unrealized Losses	1,157	112
U.S. Government, Government agencies and Government-sponsored enterprises
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	2,095	898
Gross Unrealized Losses	116	8
AAA
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	993	368
Gross Unrealized Losses	105	6
AA
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	2,809	875
Gross Unrealized Losses	269	17
A
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	3,300	1,516
Gross Unrealized Losses	205	23
BBB
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	6,073	1,812
Gross Unrealized Losses	392	42
Non-investment grade
Debt Securities, Available-for-sale [Line Items]
Estimated Fair Value	1,254	596
Gross Unrealized Losses	$ 70	$ 16