Long-Term Debt (Narrative) (Detail)			6 Months Ended
		Feb. 20, 2015 USD ($)	Jun. 30, 2015 USD ($) agreement	Jun. 30, 2014 USD ($)	Feb. 19, 2015 USD ($)	Dec. 31, 2014 USD ($)
Debt Instrument [Line Items]
Long term debt			$ 1,939,427,000			$ 1,979,565,000
Debt issuance costs			3,120,000	$ 125,000
Credit Agreement [Member]
Debt Instrument [Line Items]
Credit facility			$ 1,200,000,000
Maturity date			Jan. 24, 2020
Master Note Purchase Agreement [Member]
Debt Instrument [Line Items]
Long term debt			$ 600,000,000
Maximum limit on certain restricted payments, including dividends and share repurchases		$ 300,000,000			$ 200,000,000
Maximum limit of aggregate principal amount of notes outstanding			1,250,000,000
Maximum limit of aggregate amount of permitted investments in other lines of business		$ 100,000,000			$ 50,000,000
Third Supplement to Master Note Purchase Agreement [Member] | Scenario, Plan [Member]
Debt Instrument [Line Items]
Aggregate principal amount			$ 500,000,000
Number of notes tranches | agreement			2
2015A Note First Tranche [Member] | Scenario, Plan [Member]
Debt Instrument [Line Items]
Maturity date			Aug. 20, 2022
Interest rate			3.09%
Aggregate principal amount			$ 125,000,000
2015A Note Second Tranche [Member] | Scenario, Plan [Member]
Debt Instrument [Line Items]
Maturity date			Aug. 20, 2025
Interest rate			3.41%
Aggregate principal amount			$ 375,000,000
Minimum [Member] | Credit Agreement [Member]
Debt Instrument [Line Items]
Required interest coverage ratio			2.75
Minimum [Member] | Credit Agreement [Member] | Base Rate [Member] | Swing Line Loans [Member]
Debt Instrument [Line Items]
Margin rate for loans			0.00%
Minimum [Member] | Credit Agreement [Member] | LIBOR [Member] | Letter of Credit [Member]
Debt Instrument [Line Items]
Margin rate for loans			1.00%
Maximum [Member] | Credit Agreement [Member]
Debt Instrument [Line Items]
Reguired leverage ratio during material acquisition period			3.75
Required leverage ratio			3.50
Revolving credit term loan maximum borrowing capacity			$ 2,300,000,000
Maximum [Member] | Credit Agreement [Member] | Letter of Credit [Member]
Debt Instrument [Line Items]
Revolving credit term loan maximum borrowing capacity			250,000,000
Maximum [Member] | Credit Agreement [Member] | Swing Line Loans [Member]
Debt Instrument [Line Items]
Revolving credit term loan maximum borrowing capacity			$ 35,000,000
Maximum [Member] | Credit Agreement [Member] | Base Rate [Member] | Swing Line Loans [Member]
Debt Instrument [Line Items]
Margin rate for loans			0.50%
Maximum [Member] | Credit Agreement [Member] | LIBOR [Member] | Letter of Credit [Member]
Debt Instrument [Line Items]
Margin rate for loans			1.50%
Maximum [Member] | Master Note Purchase Agreement [Member]
Debt Instrument [Line Items]
Required leverage ratio		3.0
Revolver Under Prior Credit Agreement [Member]
Debt Instrument [Line Items]
Long term debt						680,000,000
Maturity date			May 04, 2018
Term Loan Facility [Member]
Debt Instrument [Line Items]
Long term debt						660,000,000
Maturity date			Oct. 25, 2017
Term Loan Facility [Member] | Credit Agreement [Member]
Debt Instrument [Line Items]
Long term debt	[1]		$ 800,000,000
Aggregate principal amount			800,000,000
Senior Notes due 2015 [Member]
Debt Instrument [Line Items]
Long term debt			$ 175,000,000			$ 175,000,000
Interest rate			6.22%			6.22%
Senior Notes due 2019 [Member]
Debt Instrument [Line Items]
Long term debt			$ 175,000,000			$ 175,000,000
Interest rate			5.25%			5.25%
Senior Notes due 2016 [Member]
Debt Instrument [Line Items]
Long term debt			$ 100,000,000			$ 100,000,000
Interest rate			3.30%			3.30%
Senior Notes due 2018 [Member]
Debt Instrument [Line Items]
Long term debt			$ 50,000,000			$ 50,000,000
Interest rate			4.00%			4.00%
Senior Notes due 2021 [Member]
Debt Instrument [Line Items]
Long term debt			$ 100,000,000			$ 100,000,000
Interest rate			4.64%			4.64%
Tax-exempt Bonds [Member]
Debt Instrument [Line Items]
Long term debt	[1]		$ 31,430,000			$ 31,430,000
2015A Notes [Member]
Debt Instrument [Line Items]
Margin rate for loans			0.50%
Senior Notes | Master Note Purchase Agreement [Member] | Scenario, Plan [Member]
Debt Instrument [Line Items]
Long term debt			$ 1,100,000,000

[1] Interest rates in the table above represent the range of interest rates incurred during the six month period ended June 30, 2015.