CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 1,721	$ 1,652	$ 1,045
Other comprehensive loss:
Net unrealized derivative instrument losses arising during the periods, net of income taxes of ($11), ($9) and ($38), respectively	(33)	(14)	(62)
Reclassification adjustment for net derivative losses (gains) included in net income, net of income taxes of $10, ($9) and ($22), respectively	33	(16)	(36)
Net unrealized debt securities losses arising during the periods, net of income taxes of ($79), ($4) and ($82), respectively	(239)	(6)	(139)
Other-than-temporary impairment not recognized in earnings on debt securities, net of income taxes of ($1), $0 and ($10), respectively	(3)	0	(17)
Reclassification of net debt securities gains to net income, net of income taxes of ($4), ($2) and ($2), respectively	(12)	(2)	(2)
Employee benefit plans:
Actuarial (loss) gain, net of income taxes of ($14), $12 and ($20), respectively	(35)	19	(34)
Amortization of actuarial loss, net of income taxes of $3, $5 and $6, respectively	14	13	10
Amortization of prior service cost, net of income taxes of $0, $0 and $0, respectively	(1)	(1)	(1)
Total other comprehensive loss, net of income taxes	(276)	(7)	(281)
Total comprehensive income	$ 1,445	$ 1,645	$ 764