Parent Company Financial Statements - Statements of Income of Parent Company Only (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Condensed Income Statements, Captions [Line Items]
Interest income	$ 1,005	$ 1,130	$ 1,247
Interest expense	98	208	330
Income Before Income Taxes	503	343	471
Income tax benefit	(98)	(57)	(84)
Net income	405	286	387
Parent Company
Condensed Income Statements, Captions [Line Items]
Dividend income from subsidiaries:	220	304	181
Interest income	13	6	0
Total Income	233	310	181
Interest expense	25	25	19
Other expenses	17	18	18
Total Expenses	42	43	37
Income Before Income Taxes	191	267	144
Income tax benefit	7	7	7
Income after income taxes	198	274	151
Equity in undistributed income (loss) of subsidiaries:	207	12	236
Net income	405	286	387
Parent Company | Bank
Condensed Income Statements, Captions [Line Items]
Dividend income from subsidiaries:	215	300	179
Equity in undistributed income (loss) of subsidiaries:	207	15	236
Parent Company | Non-Bank
Condensed Income Statements, Captions [Line Items]
Dividend income from subsidiaries:	5	4	2
Equity in undistributed income (loss) of subsidiaries:	$ 0	$ (3)	$ 0