Benefit Plans and Other Postretirement Benefits, Defined contribution plans (Details) - United States - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Defined Contribution Plan Disclosure
Contributions to U.S. defined contribution plans by the Company, maximum percentage of eligible compensation	6.00%		5.00%
Matching contributions to U.S. defined contribution plans by the Company	$ 4.0	$ 2.3