CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 243	$ 190	$ 466	$ 399
Other comprehensive income (loss):
Net unrealized derivative instrument gains (losses) arising during the periods, net of income taxes of $8, ($3), $29 and $36, respectively	13	(5)	46	60
Reclassification adjustment for net derivative gains included in net income, net of income taxes of ($4), ($1), ($10) and ($2), respectively	(9)	(2)	(17)	(4)
Net unrealized securities available for sale gains (losses) arising during the periods, net of income taxes of $39, ($66), $131 and ($12), respectively	64	(110)	218	(20)
Other-than-temporary impairment not recognized in earnings on securities, net of income taxes of $2, $0, ($13) and ($11), respectively	4	1	(21)	(18)
Reclassification of net securities losses (gains) to net income, net of income taxes of $1, ($2), ($2) and ($5), respectively	2	(5)	(3)	(9)
Defined benefit pension plans:
Amortization of actuarial loss, net of income taxes of $1, $2, $3 and $3, respectively	3	2	5	4
Total other comprehensive income (loss), net of income taxes	77	(119)	228	13
Total comprehensive income	$ 320	$ 71	$ 694	$ 412