Investment Securities (Contractual Maturities Debt Securities) (Details) - USD ($) $ in Millions	Jun. 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	$ 138
Held-to-maturity, Due in one year or less, Estimated fair value	138
Held-to-maturity, Due after one year through five years, Amortized cost	258
Held-to-maturity, Due after one year through five years, Estimated fair value	259
Held-to-maturity, Due after five years through ten years, Amortized cost	155
Held-to-maturity, Due after five years through ten years, Estimated fair value	158
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Amortized Cost	144
Held-to-maturity, Due after ten years, Estimated fair value	143
Held-to-maturity, Amortized cost	695
Held-to-maturity, fair value	698
Available-for-sale, Due in one year or less, Amortized cost	177
Available-for-sale, Due in one year or less, Estimated fair value	177
Available-for-sale, Due after one year through five years, Amortized cost	633
Available-for-sale, Due after one year through five years, Estimated fair value	636
Available-for-sale, Due after five years through ten years, Amortized cost	2,824
Available-for-sale, Due after five years through ten years, Estimated fair value	2,835
Available-for-sale, Due after ten years, Amortized cost	11,025
Available-for-sale, Due after ten years, Estimated fair value	11,024
Available-for-sale, Amortized cost	14,659	$ 15,040
Available-for-sale, Estimated fair value	$ 14,672	$ 14,737