Fair Values (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Investment securities:
Equity securities and other	$ 49	$ 49
Debt securities	3,201	3,108
Derivatives	235	765
Total assets	3,485	3,922
Level 1 [Member]
Investment securities:
Equity securities and other	1	1
Debt securities	1,118	460
Derivatives	0	0
Total assets	1,119	461
Level 2 [Member]
Investment securities:
Equity securities and other	48	48
Debt securities	2,083	2,648
Derivatives	235	765
Total assets	2,366	3,461
Level 3 [Member]
Investment securities:
Equity securities and other	0	0
Debt securities	0	0
Derivatives	0	0
Total assets	$ 0	$ 0