CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 453	$ 425	$ 892	$ 813
Other comprehensive income (loss):
Net unrealized derivative instrument gains (losses) arising during the periods, net of income taxes of $23, ($4), $36 and ($22), respectively	68		107
Net unrealized derivative instrument gains (losses) arising during the periods, net of income taxes of $23, ($4), $36 and ($22), respectively, before 2017-12 adoption		(13)		(65)
Reclassification adjustment for net derivative losses included in net income, net of income taxes of $4, $3, $9 and $3, respectively	15		30
Reclassification adjustment for net derivative losses, included in net income, net of income taxes of $4, $3, $9, and $3, respectively, before 2017-12 adoption		6		8
Net unrealized debt securities gains (losses) arising during the periods, net of income taxes of $72, ($19), $152 and ($105), respectively	221	(60)	467	(332)
Other-than-temporary impairment not recognized in earnings on debt securities, net of income taxes of $0, $1, $0 and $0, respectively	1	0	1	(1)
Reclassification of net debt securities gains to net income, net of income taxes of ($1), $0, ($3) and ($2), respectively	(3)	(1)	(8)	(6)
Amortization of actuarial loss, net of income taxes of $1, $1, $3 and $2, respectively	3	3	6	6
Net other comprehensive (loss) income	305	(65)	603	(390)
Total comprehensive income	$ 758	$ 360	$ 1,495	$ 423