Stock-Based Compensation Plans - Valuation Assumptions for Grant Date Fair Value of Performance Awards (Detail) (Performance Shares, USD $)	9 Months Ended
	Sep. 30, 2014
Performance Shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate	0.77%
Expected annual volatility	32.50%
Grant date fair value per unit	$ 86.14	[1]

[1] Amounts granted reflect the number of performance units granted. The actual payout of shares may be between zero percent and 150% of the performance units granted depending on the total shareholder return ranking compared to the peer companies at the vesting date.