Debt (Private Placement Notes) (Details) - EUR (€) € in Millions	Sep. 30, 2017	Dec. 31, 2016	Oct. 31, 2013	Jun. 30, 2012	Jul. 27, 2010
5.00% Notes due 2020
Debt Instrument
Interest rate, stated percentage	5.00%	5.00%
3.40% Notes due 2022
Debt Instrument
Interest rate, stated percentage	3.40%	3.40%
4.00% Notes due 2027
Debt Instrument
Interest rate, stated percentage	4.00%	4.00%
4.00% Notes due 2032
Debt Instrument
Interest rate, stated percentage	4.00%	4.00%
3.75% Notes due 2033
Debt Instrument
Interest rate, stated percentage	3.75%	3.75%
3.15% Notes due 2023
Debt Instrument
Interest rate, stated percentage	3.15%	3.15%
3.15% Notes due 2023
Debt Instrument
Interest rate, stated percentage	3.15%	3.15%
Private Placement Notes
Debt Instrument
Face amount			€ 355.0	€ 325.0
Private Placement Notes | 5.00% Notes due 2020
Debt Instrument
Face amount					€ 200.0
Interest rate, stated percentage	5.00%	5.00%			5.00%
Private Placement Notes | 3.40% Notes due 2022
Debt Instrument
Face amount				€ 150.0
Interest rate, stated percentage	3.40%	3.40%		3.40%
Private Placement Notes | 4.00% Notes due 2027
Debt Instrument
Face amount				€ 75.0
Interest rate, stated percentage	4.00%	4.00%		4.00%
Private Placement Notes | 4.00% Notes due 2032
Debt Instrument
Face amount				€ 100.0
Interest rate, stated percentage	4.00%	4.00%		4.00%
Private Placement Notes | 3.75% Notes due 2033
Debt Instrument
Face amount			€ 100.0
Interest rate, stated percentage	3.75%	3.75%	3.75%
Private Placement Notes | 3.15% Notes due 2023
Debt Instrument
Face amount			€ 130.0
Interest rate, stated percentage	3.15%	3.15%	3.15%
Private Placement Notes | 3.15% Notes due 2023
Debt Instrument
Face amount			€ 125.0
Interest rate, stated percentage	3.15%	3.15%	3.15%