Investments (Amortized Cost and Fair Value of Available-for-Sale Debt Securities by Contractual Maturity) (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Schedule of Investments [Line Items]
Due in one year or less, Amortized Cost	$ 5,372
Due after one year through five years, Amortized Cost	15,098
Due after five years through ten years, Amortized Cost	11,256
Due after ten years, Amortized Cost	5,219
Total debt securities - available-for-sale, Amortized Cost	48,668	$ 45,926
Due in one year or less, Fair Value	5,340
Due after one year through five years, Fair Value	14,183
Due after five years through ten years, Fair Value	9,898
Due after ten years, Fair Value	4,690
Debt Securities, Available-for-sale	44,352	42,321
Debt Securities, Held-to-Maturity, Amortized Cost, Maturity, Allocated and Single Maturity Date, Year One	375
Debt Securities, Held-to-Maturity, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year One Through Five	262
Debt Securities, Held-to-Maturity, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10	25
Debt Securities, Held-to-Maturity, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year 10	20
Debt Securities, Held-to-maturity	682	696
Held-to-maturity Securities, Debt Maturities, within One Year, Fair Value	372
Debt Securities, Held-to-Maturity, Fair Value, Maturity, Allocated and Single Maturity Date, after Year One Through Five	255
Debt Securities, Held-to-Maturity, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10	24
Debt Securities, Held-to-Maturity, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 10	16
Debt Securities, Held-to-maturity, Fair Value	667	679
U.S. Agency Mortgage-Backed Securities [Member]
Schedule of Investments [Line Items]
Mortgage-backed securities, Amortized Cost	8,632
Total debt securities - available-for-sale, Amortized Cost	8,632	7,379
Mortgage-backed securities, Fair Value	7,474
Debt Securities, Available-for-sale	7,474	6,586
Non-U.S. Agency Mortgage-Backed Securities [Member]
Schedule of Investments [Line Items]
Mortgage-backed securities, Amortized Cost	3,091
Total debt securities - available-for-sale, Amortized Cost	3,091	3,077
Mortgage-backed securities, Fair Value	2,767
Debt Securities, Available-for-sale	$ 2,767	$ 2,784