Intangible Assets (Intangible Assets) (Detail) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets
Gross Carrying Amount	$ 52	$ 49
Accumulated Amortization	(41)	(40)
Net Carrying Amount	11	9
Core Deposits
Finite-Lived Intangible Assets
Gross Carrying Amount	34	34
Accumulated Amortization	(28)	(27)
Net Carrying Amount	6	7
Other Intangible Assets
Finite-Lived Intangible Assets
Gross Carrying Amount	18	15
Accumulated Amortization	(13)	(13)
Net Carrying Amount	$ 5	$ 2