Earnings Per Share - Common Share Data Used for Computing Basic and Diluted Earnings Per Share (Detail) - shares shares in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Earnings Per Share [Abstract]
Number of common shares outstanding at end of period	446.5	457.9	446.5	457.9
Effect of using weighted average common shares outstanding	3.1	2.9	8.0	6.1
Weighted average basic common shares outstanding	449.6	460.8	454.5	464.0
Dilutive effect of equity-based compensation awards and other contingently issuable shares	3.1	2.8	3.0	2.4
Weighted average diluted common shares outstanding	452.7	463.6	457.5	466.4
Potentially issuable shares	11.0	12.4	11.0	12.4
Number of anti-dilutive potentially issuable shares excluded from diluted common shares outstanding	2.0	0.4	2.0	0.7