Goodwill and Other Intangible Assets - Summary of Core Deposit Intangibles, Customer Renewal Lists and Mortgage Servicing Rights (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 214	$ 211
Accumulated amortization	(147)	(132)
Net carrying amount	67	79
Core Deposit Intangibles
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	196	196
Accumulated amortization	(136)	(122)
Net carrying amount	60	74
Customer Renewal Lists
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	18	15
Accumulated amortization	(11)	(10)
Net carrying amount	$ 7	$ 5