CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 425	$ 318	$ 813	$ 638
Other comprehensive (loss) income:
Net unrealized derivative instrument (losses) gains arising during the periods, net of income taxes of ($4), $16, ($22) and $14, respectively	(13)	26	(65)	23
Reclassification adjustment for net derivative losses (gains) included in net income, net of income taxes of $3, ($2), $3 and ($6), respectively	6	(5)	8	(11)
Net unrealized debt securities (losses) gains arising during the periods, net of income taxes of ($19), $33, ($105) and $36, respectively	(60)	56	(332)	61
Other-than-temporary impairment not recognized in earnings on debt securities, net of income taxes of $1, $6, $0 and ($1), respectively	0	10	(1)	(2)
Reclassification of net debt securities (gains) losses to net income, net of income taxes of $0, $0, ($2) and ($1), respectively	(1)	1	(6)	(1)
Amortization of actuarial loss, net of income taxes of $1, $2, $2 and $4, respectively	3	2	6	5
Total other comprehensive (loss) income, net of income taxes	(65)	90	(390)	75
Total comprehensive income	$ 360	$ 408	$ 423	$ 713