STATEMENTS OF SHAREHOLDERS' EQUITY (UNAUDITED) (Parenthetical) - $ / shares	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Class A common stock
Dividends declared (in dollars per share)	$ 0.965	$ 0.965	$ 0.90	$ 0.90	$ 1.93	$ 1.80
Class B common stock
Dividends declared (in dollars per share)	$ 144.75	$ 144.75	$ 135.00	$ 135.00	$ 289.50	$ 270.00