Investment Securities (Contractual Maturities Debt Securities) (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Rolling within One Year, Amortized Cost	$ 121
Held-to-maturity, Due in one year or less, Estimated fair value	121
Held-to-maturity, Due after one year through five years, Amortized cost	241
Held-to-maturity, Due after one year through five years, Estimated fair value	242
Held-to-maturity, Due after five years through ten years, Amortized cost	171
Held-to-maturity, Due after five years through ten years, Estimated fair value	174
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Amortized Cost	125
Held-to-maturity, Due after ten years, Estimated fair value	125
Held-to-maturity, Amortized cost	658
Held-to-maturity, fair value	662
Available-for-sale, Due in one year or less, Amortized cost	172
Available-for-sale, Due in one year or less, Estimated fair value	173
Available-for-sale, Due after one year through five years, Amortized cost	642
Available-for-sale, Due after one year through five years, Estimated fair value	647
Available-for-sale, Due after five years through ten years, Amortized cost	2,631
Available-for-sale, Due after five years through ten years, Estimated fair value	2,649
Available-for-sale, Due after ten years, Amortized cost	10,549
Available-for-sale, Due after ten years, Estimated fair value	10,564
Available-for-sale, Amortized cost	13,994	$ 15,040
Available-for-sale, Estimated fair value	$ 14,033	$ 14,737