Long-Term Debt (Long-Term Debt Phantom) (Details)	12 Months Ended
	Dec. 31, 2015 USD ($)	Dec. 31, 2015 EUR (€)
EURIBOR
Long-Term Debt
Debt Instrument, Description of Variable Rate Basis	EURIBOR
LIBOR
Long-Term Debt
Debt Instrument, Description of Variable Rate Basis	LIBOR
$1.4 billion unsecured revolving credit facility, LIBOR plus 1.50%, currently 1.92% and a facility fee of 0.25%, due 2020
Long-Term Debt
Long term debt, principal amount	$ 1,400,000,000
Long term debt, current interest rate (as a percent)	1.92%	1.92%
Long term debt, facility fee (as a percent)	0.25%
Margin on floating rate base (as a percent)	1.50%
Long term debt, due date (year)	2020
$1.2 billion unsecured revolving credit facility, LIBOR plus 1.50%, currently 1.89% and a facility fee of 0.25%, due 2018
Long-Term Debt
Long term debt, principal amount	$ 1,200,000,000
Long term debt, current interest rate (as a percent)	1.89%	1.89%
Long term debt, facility fee (as a percent)	0.25%
Margin on floating rate base (as a percent)	1.50%
Long term debt, due date (year)	2018
Unsecured senior notes and senior debentures, 5.25% to 7.50%, due 2016, 2018, 2022 and 2027
Long-Term Debt
Long term debt, minimum stated interest rate	5.25%
Long term debt, maximum stated interest rate	7.50%
Unsecured senior notes and senior debentures, 5.25% to 7.50%, due 2016, 2018, 2022 and 2027 | Period 1
Long-Term Debt
Long term debt, minimum stated interest rate	5.25%
Long term debt, maximum stated interest rate	7.50%
Unsecured senior notes and senior debentures, 5.25% to 7.50%, due 2016, 2018, 2022 and 2027 | Period 2
Long-Term Debt
Long term debt, minimum stated interest rate	5.25%
Long term debt, maximum stated interest rate	7.50%
Unsecured senior notes and senior debentures, 5.25% to 7.50%, due 2016, 2018, 2022 and 2027 | Period 3
Long-Term Debt
Long term debt, minimum stated interest rate	5.25%
Long term debt, maximum stated interest rate	7.50%
Unsecured senior notes and senior debentures, 5.25% to 7.50%, due 2016, 2018, 2022 and 2027 | Period 4
Long-Term Debt
Long term debt, minimum stated interest rate	5.25%
Long term debt, maximum stated interest rate	7.50%
Unsecured senior notes and senior debentures, 5.25% to 7.50%, due 2016, 2018, 2022 and 2027 | Upper Limit | Period 1
Long-Term Debt
Long term debt, due date (year)	2016
Unsecured senior notes and senior debentures, 5.25% to 7.50%, due 2016, 2018, 2022 and 2027 | Upper Limit | Period 2
Long-Term Debt
Long term debt, due date (year)	2018
Unsecured senior notes and senior debentures, 5.25% to 7.50%, due 2016, 2018, 2022 and 2027 | Upper Limit | Period 3
Long-Term Debt
Long term debt, due date (year)	2022
Unsecured senior notes and senior debentures, 5.25% to 7.50%, due 2016, 2018, 2022 and 2027 | Upper Limit | Period 4
Long-Term Debt
Long term debt, due date (year)	2027
$742.1 million unsecured senior notes, LIBOR plus 1.30%, currently 1.83%, due through 2027
Long-Term Debt
Long term debt, principal amount | €		€ 742,100,000.0
Long term debt, current interest rate (as a percent)	1.83%	1.83%
Margin on floating rate base (as a percent)	1.30%
Long term debt, due date (year)	2027
$530 million unsecured term loan, LIBOR plus 0.51%, due through 2015
Long-Term Debt
Long term debt, principal amount	$ 530,000,000
Margin on floating rate base (as a percent)	0.51%
Long term debt, due date (year)	2015
$519 million unsecured term loan, LIBOR plus 0.45%, currently 0.98%, due through 2020
Long-Term Debt
Long term debt, principal amount	$ 519,000,000
Long term debt, current interest rate (as a percent)	0.98%	0.98%
Margin on floating rate base (as a percent)	0.45%
Long term debt, due date (year)	2020
$420 million unsecured term loan, 5.41%, due through 2021
Long-Term Debt
Long term debt, principal amount	$ 420,000,000
Long term debt, stated interest rate (as a percent)	5.41%	5.41%
Long term debt, due date (year)	2021
$420 million unsecured term loan, LIBOR plus 1.85%, currently 2.38%, due through 2021
Long-Term Debt
Long term debt, principal amount	$ 420,000,000
Long term debt, current interest rate (as a percent)	2.38%	2.38%
Margin on floating rate base (as a percent)	1.85%
Long term debt, due date (year)	2021
€159.4 million unsecured term loan, EURIBOR plus 1.58%, currently 1.60%, due through 2021
Long-Term Debt
Long term debt, principal amount | €		€ 159,400,000.0
Long term debt, current interest rate (as a percent)	1.60%	1.60%
Margin on floating rate base (as a percent)	1.58%
Long term debt, due date (year)	2021
$524.5 million unsecured term loan, LIBOR plus 0.50%, currently 0.96%, due through 2021
Long-Term Debt
Long term debt, principal amount	$ 524,500,000.0
Long term debt, current interest rate (as a percent)	0.96%	0.96%
Margin on floating rate base (as a percent)	0.50%
Long term debt, due date (year)	2021
$566.1 million unsecured term loan, LIBOR plus 0.37%, currently 0.89%, due through 2022
Long-Term Debt
Long term debt, principal amount	$ 566,100,000.0
Long term debt, current interest rate (as a percent)	0.89%	0.89%
Margin on floating rate base (as a percent)	0.37%
Long term debt, due date (year)	2022
$1.1 billion unsecured term loan, LIBOR plus 1.85%, currently 2.38%, due through 2022
Long-Term Debt
Long term debt, principal amount	$ 1,100,000,000
Long term debt, current interest rate (as a percent)	2.38%	2.38%
Margin on floating rate base (as a percent)	1.85%
Long term debt, due date (year)	2022
$632.0 million unsecured term loan, LIBOR plus 0.40%, currently 0.86%, due through 2023
Long-Term Debt
Long term debt, principal amount	$ 632,000,000
Long term debt, current interest rate (as a percent)	0.86%	0.86%
Margin on floating rate base (as a percent)	0.40%
Long term debt, due date (year)	2023
$673.5 million unsecured term loan, LIBOR plus 0.40%, currently 0.93%, due through 2024
Long-Term Debt
Long term debt, principal amount	$ 673,500,000.0
Long term debt, current interest rate (as a percent)	0.93%	0.93%
Margin on floating rate base (as a percent)	0.40%
Long term debt, due date (year)	2024
$65.0 million unsecured term loan, LIBOR plus 1.75%, currently 2.17%, due through 2019
Long-Term Debt
Long term debt, principal amount	$ 65,000,000
Long term debt, current interest rate (as a percent)	2.17%	2.17%
Margin on floating rate base (as a percent)	1.75%
Long term debt, due date (year)	2019
$1.0 million unsecured term loan, 3.00%, due through 2015
Long-Term Debt
Long term debt, principal amount	$ 1,000,000,000
Long term debt, stated interest rate (as a percent)	3.00%	3.00%
Long term debt, due date (year)	2015
$380.0 million unsecured term loan, LIBOR plus 1.75%, currently 2.17%, due through 2018
Long-Term Debt
Long term debt, principal amount	$ 380,000,000
Long term debt, current interest rate (as a percent)	2.17%	2.17%
Margin on floating rate base (as a percent)	1.75%
Long term debt, due date (year)	2018
$380.0 million unsecured term loan, LIBOR plus 1.75%, currently 2.17%, due through 2018 | LIBOR
Long-Term Debt
Margin on floating rate base (as a percent)	1.75%
$791.1 million unsecured term loan, LIBOR plus 1.30%, currently 1.83%, due through 2026
Long-Term Debt
Long term debt, principal amount	$ 791,100,000.0
Long term debt, current interest rate (as a percent)	1.83%	1.83%
Margin on floating rate base (as a percent)	1.30%
Long term debt, due date (year)	2026
$290.0 million unsecured term loan, LIBOR plus 1.75%, currently 2.17%, due 2018
Long-Term Debt
Long term debt, principal amount	$ 290,000,000
Long term debt, current interest rate (as a percent)	2.17%	2.17%
Margin on floating rate base (as a percent)	1.75%
Long term debt, due date (year)	2018
€365 million unsecured term loan, EURIBOR plus 1.75%, currently 1.75%, due 2017
Long-Term Debt
Long term debt, principal amount | €		€ 365,000,000
Long term debt, current interest rate (as a percent)	1.75%	1.75%
Margin on floating rate base (as a percent)	1.75%
Long term debt, due date (year)	2017
$7.3 million unsecured term loan, LIBOR plus 2.5%, currently 3.02%, due through 2023
Long-Term Debt
Long term debt, principal amount	$ 7,300,000.0
Long term debt, current interest rate (as a percent)	3.02%	3.02%
Margin on floating rate base (as a percent)	2.50%
Long term debt, due date (year)	2023
$30.3 million unsecured term loan, LIBOR plus 3.75%, currently 4.24%, due through 2021
Long-Term Debt
Long term debt, principal amount	$ 30,300,000.0
Long term debt, current interest rate (as a percent)	4.24%	4.24%
Margin on floating rate base (as a percent)	3.75%
Long term debt, due date (year)	2021