Consolidated and Combined Statements of Changes in Equity (Parenthetical) - $ / shares	3 Months Ended								6 Months Ended		12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2017	Jul. 02, 2017	Dec. 31, 2018	Dec. 31, 2017
Special dividend
Dividends (in dollars per share)										$ 17.5
Special dividend | Class A
Dividends (in dollars per share)												$ 17.5
Cash dividend
Dividends (in dollars per share)									$ 0.35
Cash dividend | Class A
Dividends (in dollars per share)	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.17	$ 0	$ 0			$ 0.72	$ 0.35