Fair Values (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Investment securities:
Equity securities and other	$ 48	$ 49
Debt securities	3,111	3,108
Derivative assets	210	765
Total assets	3,369	3,922
Liabilities
Derivative liabilities	218	280
Total liabilities	218	280
Level 1 [Member]
Investment securities:
Equity securities and other	1	1
Debt securities	1,045	460
Derivative assets	0	0
Total assets	1,046	461
Liabilities
Derivative liabilities	0	0
Total liabilities	0	0
Level 2 [Member]
Investment securities:
Equity securities and other	47	48
Debt securities	2,066	2,648
Derivative assets	210	765
Total assets	2,323	3,461
Liabilities
Derivative liabilities	218	280
Total liabilities	218	280
Level 3 [Member]
Investment securities:
Equity securities and other	0	0
Debt securities	0	0
Derivative assets	0	0
Total assets	0	0
Liabilities
Derivative liabilities	0	0
Total liabilities	$ 0	$ 0