Description of Business and Accounting Policies Calculation of Diluted Shares (Detail) In Millions, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accounting Policies [Abstract]
Shares used in computation of basic earnings per share	464	[1]	463	[1]	461	[1]	460	[1]	458	[1]	457	[1]	456	[1]	455	[1]	462	457	453
Total dilutive effect of outstanding stock awards																	0	8	0
Shares used in computation of diluted earnings per share	472	[1]	463	[1]	461	[1]	468	[1]	467	[1]	457	[1]	456	[1]	463	[1]	462	465	453

[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.