Stockholders' Equity - Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018		Mar. 31, 2018	Dec. 31, 2017
Summary of accumulated other comprehensive income/(loss) [Line Items]
Total accumulated other comprehensive loss	$ 16,047,831	$ 15,586,599	[1]	$ 15,059,326	$ 14,925,452
Foreign currency translation
Summary of accumulated other comprehensive income/(loss) [Line Items]
Total accumulated other comprehensive loss	(795,173)	(868,006)
Derivative instruments
Summary of accumulated other comprehensive income/(loss) [Line Items]
Total accumulated other comprehensive loss	651,095	738,777
Actuarial losses
Summary of accumulated other comprehensive income/(loss) [Line Items]
Total accumulated other comprehensive loss	(540)	(540)
Total accumulated other comprehensive loss
Summary of accumulated other comprehensive income/(loss) [Line Items]
Total accumulated other comprehensive loss	$ (144,618)	$ (129,769)		$ (91,253)	$ (111,465)

[1] The consolidated balance sheet at December 31, 2018 has been derived from the audited financial statements at that date but does not include all of the information and footnotes required by U.S. generally accepted accounting principles for complete financial statements.