Goodwill and Other Intangible Assets - Summary of Core Deposit Intangibles, Customer Renewal Lists and Mortgage Servicing Rights (Detail) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 211	$ 208
Accumulated amortization	(132)	(116)
Net carrying amount	79	92
Core Deposit Intangibles
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	196	196
Accumulated amortization	(122)	(107)
Net carrying amount	74	89
Customer Renewal Lists
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	15	12
Accumulated amortization	(10)	(9)
Net carrying amount	$ 5	$ 3