Intangible Assets (Intangible Assets) (Detail) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets
Gross Carrying Amount	$ 286	$ 298
Accumulated Amortization	(102)	(97)
Net Carrying Amount	184	201
Core deposit intangibles
Finite-Lived Intangible Assets
Gross Carrying Amount	229	229
Accumulated Amortization	(83)	(70)
Net Carrying Amount	146	159
Customer Relationships
Finite-Lived Intangible Assets
Gross Carrying Amount	29	29
Accumulated Amortization	(6)	(6)
Net Carrying Amount	23	23
Noncompete Agreements
Finite-Lived Intangible Assets
Gross Carrying Amount	3	13
Accumulated Amortization	(1)	(11)
Net Carrying Amount	2	2
Other Intangible Assets
Finite-Lived Intangible Assets
Gross Carrying Amount	4	4
Accumulated Amortization	(1)	(1)
Net Carrying Amount	3	3
Operating lease intangibles
Finite-Lived Intangible Assets
Gross Carrying Amount	21	23
Accumulated Amortization	(11)	(9)
Net Carrying Amount	$ 10	$ 14