CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 318	$ 243	$ 638	$ 466
Other comprehensive income:
Net unrealized derivative instrument gains arising during the periods, net of income tax expense of $16, $8, $14 and $29, respectively	26	13	23	46
Reclassification adjustment for net derivative gains included in net income, net of income taxes of ($2), ($4), ($6) and ($10), respectively	(5)	(9)	(11)	(17)
Net unrealized securities gains arising during the periods, net of income taxes of $33, $39, $36 and $131, respectively	56	64	61	218
Other-than-temporary impairment not recognized in earnings on securities, net of income taxes of $6, $2, ($1) and ($13), respectively	10	4	(2)	(21)
Reclassification of net securities losses (gains) to net income, net of income taxes of $0, $1, ($1) and ($2), respectively	1	2	(1)	(3)
Employee Benefit Plans: Amortization of actuarial loss, net of income taxes of $2, $1, $4 and $3, respectively	2	3	5	5
Total other comprehensive income, net of income taxes	90	77	75	228
Total comprehensive income	$ 408	$ 320	$ 713	$ 694