CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 443	$ 348	$ 1,256	$ 986
Other comprehensive (loss) income:
Net unrealized derivative instrument (losses) gains arising during the periods, net of income taxes of ($9), ($1), ($31) and $13, respectively	(26)	(1)	(91)	22
Reclassification adjustment for net derivative losses (gains) included in net income, net of income taxes of $3, ($2), $6 and ($8), respectively	11	(2)	19	(13)
Net unrealized debt securities (losses) gains arising during the periods, net of income taxes of ($34), $8, ($139) and $44, respectively	(95)	13	(427)	74
Other-than-temporary impairment not recognized in earnings on debt securities, net of income taxes of ($1), $0, ($1) and ($1), respectively	0	0	(1)	(2)
Reclassification of net debt securities gains to net income, net of income taxes of $0, $0, ($2) and ($1), respectively	(2)	(1)	(8)	(2)
Amortization of actuarial loss, net of income taxes of $1, $2, $3 and $6, respectively	4	3	10	8
Total other comprehensive (loss) income, net of income taxes	(108)	12	(498)	87
Total comprehensive income	$ 335	$ 360	$ 758	$ 1,073