Investment Securities (Contractual Maturities Debt Securities) (Details) $ in Millions	Dec. 31, 2019 USD ($)
Investments [Abstract]
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Rolling within One Year, Amortized Cost	$ 101
Held-to-maturity, Due in one year or less, Estimated fair value	102
Held-to-maturity, Due after one year through five years, Estimated fair value	216
Held-to-maturity, Due after five years through ten years, Estimated fair value	159
Held-to-maturity, Due after ten years, Estimated fair value	120
Held-to-maturity, Amortized cost	592
Held-to-maturity, fair value	597
Available-for-sale, Due in one year or less, Amortized cost	122
Available-for-sale, Due in one year or less, Estimated fair value	122
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Rolling after One Through Five Years, Amortized Cost	215
Available-for-sale, Due after one year through five years, Amortized cost	718
Available-for-sale, Due after one year through five years, Estimated fair value	726
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Rolling after Five Through Ten Years, Amortized Cost	156
Available-for-sale, Due after five years through ten years, Amortized cost	2,434
Available-for-sale, Due after five years through ten years, Estimated fair value	2,450
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Amortized Cost	120
Available-for-sale, Due after ten years, Amortized cost	10,412
Available-for-sale, Due after ten years, Estimated fair value	10,427
Available-for-sale, Amortized cost	13,686
Available-for-sale, Estimated fair value	$ 13,725