Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Statement of Comprehensive Income [Abstract]
Net income for the period	$ 240	$ 175	$ 916	$ 255
Other comprehensive income (loss), net of tax:
Net unrealized holding gains (losses) on investment securities	(95)	(13)	(225)	229
Net unrealized gains (losses) on other noninterest-bearing investments	0	2	3	(4)
Net unrealized holding gains (losses) on derivative instruments	(4)	(1)	(4)	75
Reclassification adjustment for increase in interest income recognized in earnings on derivative instruments	(12)	(11)	(35)	(24)
Reclassification to earnings for termination of pension plan	0	0	0	13
Other comprehensive income (loss)	(111)	(23)	(261)	289
Comprehensive income	$ 129	$ 152	$ 655	$ 544