Fair Value Measurements (Fair Value of Debt) (Detail) - USD ($) $ in Millions		Mar. 31, 2017	Dec. 31, 2016
Synthetic bonds due 2021 | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value of debt	[1]	$ 633.6	$ 663.2
Synthetic bonds due 2021 | Carrying Amount
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value of debt	[2]	$ 441.5	$ 428.0
2.00% Senior Notes due 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Senior notes, interest rate, as a percent		2.00%	2.00%
2.00% Senior Notes due 2017 | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value of debt	[1]	$ 300.6
2.00% Senior Notes due 2017 | Carrying Amount
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value of debt	[2]	$ 300.0
3.45% Senior Notes due 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Senior notes, interest rate, as a percent		3.45%	3.45%
3.45% Senior Notes due 2022 | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value of debt	[1]	$ 506.8
3.45% Senior Notes due 2022 | Carrying Amount
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value of debt	[2]	$ 500.0
5.00% Notes due 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Senior notes, interest rate, as a percent		5.00%	5.00%
5.00% Notes due 2020 | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value of debt	[1]	$ 240.8	$ 237.7
5.00% Notes due 2020 | Carrying Amount
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value of debt	[2]	$ 215.0	$ 209.7
3.40% Notes due 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Senior notes, interest rate, as a percent		3.40%	3.40%
3.40% Notes due 2022 | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value of debt	[1]	$ 178.0	$ 177.6
3.40% Notes due 2022 | Carrying Amount
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value of debt	[2]	$ 161.9	$ 158.0
3.15% Notes due 2023
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Senior notes, interest rate, as a percent		3.15%	3.15%
3.15% Notes due 2023 | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value of debt	[1]	$ 154.5	$ 152.0
3.15% Notes due 2023 | Carrying Amount
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value of debt	[2]	$ 139.5	$ 136.1
3.15% Notes due 2023
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Senior notes, interest rate, as a percent		3.15%	3.15%
3.15% Notes due 2023 | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value of debt	[1]	$ 146.5	$ 142.5
3.15% Notes due 2023 | Carrying Amount
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value of debt	[2]	$ 134.8	$ 131.4
4.00% Notes due 2027
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Senior notes, interest rate, as a percent		4.00%	4.00%
4.00% Notes due 2027 | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value of debt	[1]	$ 90.9	$ 89.5
4.00% Notes due 2027 | Carrying Amount
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value of debt	[2]	$ 81.0	$ 79.0
4.00% Notes due 2032
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Senior notes, interest rate, as a percent		4.00%	4.00%
4.00% Notes due 2032 | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value of debt	[1]	$ 123.3	$ 122.1
4.00% Notes due 2032 | Carrying Amount
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value of debt	[2]	$ 103.8	$ 101.2
3.75% Notes due 2033
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Senior notes, interest rate, as a percent		3.75%	3.75%
3.75% Notes due 2033 | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value of debt	[1]	$ 108.2	$ 104.1
3.75% Notes due 2033 | Carrying Amount
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value of debt	[2]	$ 104.4	$ 101.8

[1] Restated balances related to adjustments to equity interests due to the use of incorrect foreign exchange rates.

[2] Carrying amounts are shown net of unamortized debt discounts and premiums and unamortized debt issuance costs.