Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Statement of Comprehensive Income [Abstract]
Net income for the period	$ 354	$ 66	$ 676	$ 80
Other comprehensive income (loss), net of tax:
Net unrealized holding gains (losses) on investment securities	34	94	(130)	242
Net unrealized gains (losses) on other noninterest-bearing investments	1	(8)	3	(6)
Net unrealized holding gains on derivative instruments	3	7	0	76
Reclassification adjustment for increase in interest income recognized in earnings on derivative instruments	(11)	(10)	(23)	(13)
Reclassification to earnings for termination of pension plan	0	13	0	13
Other comprehensive income (loss)	27	96	(150)	312
Comprehensive income	$ 381	$ 162	$ 526	$ 392