Investments (Amortized Cost and Fair Value of Available-for-Sale Debt Securities by Contractual Maturity) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Schedule of Investments [Line Items]
Due in one year or less, Amortized Cost	$ 4,430
Due after one year through five years, Amortized Cost	14,686
Due after five years through ten years, Amortized Cost	10,690
Due after ten years, Amortized Cost	4,908
Total debt securities - available-for-sale, Amortized Cost	47,010	$ 47,451
Due in one year or less, Fair Value	4,398
Due after one year through five years, Fair Value	14,061
Due after five years through ten years, Fair Value	9,813
Due after ten years, Fair Value	4,626
Debt Securities, Available-for-sale	44,132	44,895
Debt Securities, Held-to-Maturity, Amortized Cost, Maturity, Allocated and Single Maturity Date, Year One	336
Debt Securities, Held-to-Maturity, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year One Through Five	219
Debt Securities, Held-to-Maturity, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10	24
Debt Securities, Held-to-Maturity, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year 10	18
Debt Securities, Held-to-maturity	597	603
Held-to-maturity Securities, Debt Maturities, within One Year, Fair Value	334
Debt Securities, Held-to-Maturity, Fair Value, Maturity, Allocated and Single Maturity Date, after Year One Through Five	216
Debt Securities, Held-to-Maturity, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10	23
Debt Securities, Held-to-Maturity, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 10	16
Debt Securities, Held-to-maturity, Fair Value	589	596
U.S. Agency Mortgage-Backed Securities [Member]
Schedule of Investments [Line Items]
Mortgage-backed securities, Amortized Cost	9,395
Total debt securities - available-for-sale, Amortized Cost	9,395	8,982
Mortgage-backed securities, Fair Value	8,552
Debt Securities, Available-for-sale	8,552	8,296
Non-U.S. Agency Mortgage-Backed Securities [Member]
Schedule of Investments [Line Items]
Mortgage-backed securities, Amortized Cost	2,901
Total debt securities - available-for-sale, Amortized Cost	2,901	3,023
Mortgage-backed securities, Fair Value	2,682
Debt Securities, Available-for-sale	$ 2,682	$ 2,786