CONSOLIDATED STATEMENTS OF EQUITY (Parenthetical) - $ / shares	1 Months Ended							12 Months Ended
	Nov. 30, 2018	Aug. 31, 2018	Nov. 30, 2017	Aug. 31, 2017	May 31, 2017	Nov. 30, 2016	Aug. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Dividends declared per share (USD per share)	$ 0.20	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.18
Dividends paid per share (USD per share)								$ 0.74	$ 0.72
Class A Common Stock
Dividends declared per share (USD per share)								0.74	0.72	$ 0.71
Dividends paid per share (USD per share)								0.74	0.72	0.71
Class B Common Stock
Dividends declared per share (USD per share)								0.74	0.72	0.71
Dividends paid per share (USD per share)								$ 0.74	$ 0.72	$ 0.71