Description of Business and Accounting Policies Calculation of Diluted Shares (Detail) - shares shares in Millions	3 Months Ended																12 Months Ended
	Dec. 31, 2015	[1]	Sep. 30, 2015	[1]	Jun. 30, 2015	[1]	Mar. 31, 2015	[1]	Dec. 31, 2014	[1]	Sep. 30, 2014	[1]	Jun. 30, 2014	[1]	Mar. 31, 2014	[1]	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accounting Policies [Abstract]
Shares used in computation of basic earnings per share	470		468		467		465		464		463		461		460		467	462	457
Total dilutive effect of outstanding stock awards																	10	0	8
Shares used in computation of diluted earnings per share	481		478		476		465		472		463		461		468		477	462	465

[1] The sum of quarterly amounts, including per share amounts, may not equal amounts reported for year-to-date periods. This is due to the effects of rounding and changes in the number of weighted-average shares outstanding for each period.