Fair Values (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Investment securities:
Equity securities and other	$ 49	$ 49
Debt securities	3,512	3,108
Derivatives	230	765
Total assets	3,791	3,922
Level 1 [Member]
Investment securities:
Equity securities and other	1	1
Debt securities	1,136	460
Derivatives	0	0
Total assets	1,137	461
Level 2 [Member]
Investment securities:
Equity securities and other	48	48
Debt securities	2,376	2,648
Derivatives	230	765
Total assets	2,654	3,461
Level 3 [Member]
Investment securities:
Equity securities and other	0	0
Debt securities	0	0
Derivatives	0	0
Total assets	$ 0	$ 0