CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 1,652	$ 1,045	$ 840
Other comprehensive loss:
Net unrealized derivative instrument (losses) gains arising during the periods, net of income taxes of ($9), ($38) and $57, respectively	(14)	(62)	93
Reclassification adjustment for net derivative gains included in net income, net of income taxes of ($9), ($22), and ($9), respectively	(16)	(36)	(14)
Net unrealized securities losses arising during the periods, net of income taxes of ($4), ($82), and ($38), respectively	(6)	(139)	(66)
Other-than-temporary impairment not recognized in earnings on securities, net of income taxes of $0, ($10), and ($14), respectively	0	(17)	(22)
Reclassification of net securities gains to net income, net of income taxes of ($2), ($2) and ($8), respectively	(2)	(2)	(14)
Employee benefit plans:
Actuarial gain (loss), net of income taxes of $12, ($20) and ($3), respectively	19	(34)	(3)
Amortization of actuarial loss, net of income taxes of $5, $6 and $3, respectively	13	10	12
Amortization of prior service cost, net of income taxes of $0, $0 and $0, respectively	(1)	(1)	(1)
Total other comprehensive loss, net of income taxes	(7)	(281)	(15)
Total comprehensive income	$ 1,645	$ 764	$ 825