Intangible Assets (Intangible Assets) (Detail) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets
Gross Carrying Amount	$ 87	$ 69
Accumulated Amortization	(47)	(42)
Net Carrying Amount	40	27
Core Deposits
Finite-Lived Intangible Assets
Gross Carrying Amount	34	34
Accumulated Amortization	(30)	(29)
Net Carrying Amount	4	5
Customer Relationships
Finite-Lived Intangible Assets
Gross Carrying Amount	32	16
Accumulated Amortization	(3)	0
Net Carrying Amount	29	16
Noncompete Agreements
Finite-Lived Intangible Assets
Gross Carrying Amount	14	13
Accumulated Amortization	(11)	(10)
Net Carrying Amount	3	3
Other Intangible Assets
Finite-Lived Intangible Assets
Gross Carrying Amount	7	6
Accumulated Amortization	(3)	(3)
Net Carrying Amount	$ 4	$ 3