Income Taxes (Income Taxes - Additional Information) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Income Taxes
Applicable income tax expense	$ 91	$ 109	[1]
Effective tax rate	22.90%	25.10%
Net tax deficiency reclassified from capital surplus to applicable income tax expense		$ 1

[1] A net tax deficiency of $ 1 million was reclassified from capital surplus to applicable income tax expense and average common shares outstanding – diluted were adjusted at March 31, 2016, related to the early adoption of ASU 2016-09 during the fourth quarter of 2016, with an effective date of January 1, 2016.