Available-for-Sale and Held-to-Maturity Securities (Details - Maturity) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Available-for-Sale Securities, Debt Maturities [Abstract]
Available-for-sale securities, due within one year, amortized cost	$ 0
Available-for-sale securities, due within one to five years, amortized cost	363
Available-for-sale securities, due within five to ten years, amortized cost	8,713
Available-for-sale securities, due after ten years, amortized cost	11,764
Available-for-sale securities, amortized cost	20,840
Available-for-sale securities, due within one year, fair value	0
Available-for-sale securities, due within one to five years, fair value	353
Available-for-sale securities, due within five to ten years, fair value	8,647
Available-for-sale securities, due after ten years, fair value	11,672
Available-for-sale securities, fair value	20,672
Held-to-Maturity Securities, Debt Maturities [Abstract]
Held-to-maturity securities, due within one year, amortized cost	160
Held-to-maturity securities, due within one to five years, amortized cost	2,027
Held-to-maturity securities, due within five to ten years, amortized cost	5,509
Held-to-maturity securities, due after ten years, amortized cost	16,143
Held-to-maturity securities, amortized cost	23,839	$ 15,751
Held-to-maturity securities, due within one year, fair value	159
Held-to-maturity securities, due within one to five years, fair value	2,039
Held-to-maturity securities, due within five to ten years, fair value	5,486
Held-to-maturity securities, due after ten years, fair value	16,035
Held-to-maturity securities, fair value	23,719	15,716
Available-for-Sale Securities Pledged As Collateral (Textuals) [Abstract]
Available-for-sale debt securities pledged as collateral	352	6
Held-to-Maturity Securities Pledged As Collateral (Textuals) [Abstract]
Held-to-maturity debt securities pledged as collateral	$ 5,500	$ 500