CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 388	$ 320
Other comprehensive loss:
Net unrealized derivative instrument losses arising during the periods, net of income taxes of ($18) and ($2), respectively	(52)	(3)
Reclassification adjustment for net derivative losses (gains) included in net income, net of income taxes of $0 and ($4), respectively	2	(6)
Net unrealized debt securities (losses) gains arising during the periods, net of income taxes of ($86) and $3, respectively	(272)	5
Other-than-temporary impairment not recognized in earnings on debt securities, net of income taxes of ($1) and ($7), respectively	(1)	(12)
Reclassification of net debt securities gains to net income, net of income taxes of ($2) and ($1), respectively	(5)	(2)
Amortization of actuarial loss, net of income taxes of $1 and $2, respectively	3	3
Total other comprehensive loss, net of income taxes	(325)	(15)
Total comprehensive income	$ 63	$ 305