CONDENSED CONSOLIDATED STATEMENT OF COMPREHENSIVE INCOME - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018		Dec. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 172	$ 274	$ 219	$ 290	$ 270	$ 285	$ 250	$ 247	$ 955	$ 1,052		$ 614
Available-for-sale securities:
Unrealized gains (losses), net									224	(203)		137
Reclassification into earnings, net									23	(31)		(24)
Transfer of held-to-maturity securities to available-for-sale securities(1)									0	6	[1]	0
Net change from available-for-sale securities									247	(228)		113
Reclassification of foreign currency translation into earnings, net									0	0		(2)
Other comprehensive income (loss)									247	(228)		111
Comprehensive income									1,202	824		725
Transfer of held-to-maturity securities to available-for-sale securities									0	4,700		0
Other comprehensive income, transfers from held-to-maturity to available-for-sale securities, before tax									$ 0	$ 7		$ 0

[1] During the year ended December 31, 2018, securities with a carrying value of $4.7 billion and related unrealized pre-tax gain of $7 million, or $6 million net of tax, were transferred from held-to-maturity securities to available-for-sale securities as part of a one-time transition election for early adopting the new derivatives and hedge accounting guidance.