Fair Values (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Investment securities:
Equity securities	$ 47	$ 48
Debt securities	4,706	3,111
Derivative assets	510	210
Total assets	5,263	3,369
Liabilities
Derivative liabilities	279	218
Total liabilities	279	218
Level 1 [Member]
Investment securities:
Equity securities	1	1
Debt securities	2,893	1,045
Derivative assets	0	0
Total assets	2,894	1,046
Liabilities
Derivative liabilities	0	0
Total liabilities	0	0
Level 2 [Member]
Investment securities:
Equity securities	46	47
Debt securities	1,813	2,066
Derivative assets	510	210
Total assets	2,369	2,323
Liabilities
Derivative liabilities	279	218
Total liabilities	279	218
Level 3 [Member]
Investment securities:
Equity securities	0	0
Debt securities	0	0
Derivative assets	0	0
Total assets	0	0
Liabilities
Derivative liabilities	0	0
Total liabilities	$ 0	$ 0