Fair Values (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Investment securities:
Equity securities and other	$ 48	$ 48
Debt securities	3,340	3,111
Derivatives	151	210
Total assets	3,539	3,369
Level 1 [Member]
Investment securities:
Equity securities and other	1	1
Debt securities	1,661	1,045
Derivatives	0	0
Total assets	1,662	1,046
Level 2 [Member]
Investment securities:
Equity securities and other	47	47
Debt securities	1,679	2,066
Derivatives	151	210
Total assets	1,877	2,323
Level 3 [Member]
Investment securities:
Equity securities and other	0	0
Debt securities	0	0
Derivatives	0	0
Total assets	$ 0	$ 0