Intangible Assets (Intangible Assets) (Detail) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets
Gross Carrying Amount	$ 265	$ 87
Accumulated Amortization	(47)	(47)
Net Carrying Amount	218	40
Core Deposits
Finite-Lived Intangible Assets
Gross Carrying Amount	216	34
Accumulated Amortization	(31)	(30)
Net Carrying Amount	185	4
Other Intangible Assets
Finite-Lived Intangible Assets
Gross Carrying Amount	5	7
Accumulated Amortization	(2)	(3)
Net Carrying Amount	3	4
Noncompete Agreements
Finite-Lived Intangible Assets
Gross Carrying Amount	13	14
Accumulated Amortization	(11)	(11)
Net Carrying Amount	2	3
Customer Relationships
Finite-Lived Intangible Assets
Gross Carrying Amount	31	32
Accumulated Amortization	(3)	(3)
Net Carrying Amount	$ 28	$ 29