Computation of Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Computation of Earnings Per Share [Line Items]
Earnings available to common stockholders	$ 147	$ 99
Basic weighted-average shares outstanding	283.9	313.7
Effect of employee stock awards	1.0	0.9
Diluted weighted-average shares outstanding	284.9	314.6
Earnings per share, basic and diluted	$ 0.52	$ 0.32	[1]

[1] Amounts adjusted due to the adoption of Accounting Standards Update No. 2014-09, Revenue from Contracts with Customers (Topic 606) and Accounting Standards Update No. 2017-07, Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost. See Note 1 to the financial statements contained in Part I, Item 1 of this report for additional information.