CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 439	$ 388
Other comprehensive income (loss):
Net unrealized derivative instrument gains (losses) arising during the periods, net of income taxes of $13 and ($18), respectively	39	(52)
Reclassification adjustment for net derivative losses included in net income, net of income taxes of $5 and $0, respectively	15	2
Net unrealized debt securities gains (losses) arising during the periods, net of income taxes of $80 and ($86), respectively	246	(272)
Other-than-temporary impairment not recognized in earnings on debt securities, net of income taxes of $0 and ($1), respectively	0	(1)
Reclassification of net debt securities gains to net income, net of income taxes of ($2) and ($2), respectively	(5)	(5)
Amortization of actuarial loss, net of income taxes of $2 and $1, respectively	3	3
Total other comprehensive income (loss), net of income taxes	298	(325)
Total comprehensive income	$ 737	$ 63