STATEMENTS OF SHAREHOLDERS' EQUITY (UNAUDITED) (Parenthetical) - $ / shares	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Class A common stock
Dividends declared (in dollars per share)	$ 0.965	$ 0.965	$ 0.965	$ 0.90	$ 0.90	$ 0.90	$ 2.895	$ 2.70
Class B common stock
Dividends declared (in dollars per share)	$ 144.75	$ 144.75	$ 144.75	$ 135.00	$ 135.00	$ 135.00	$ 434.25	$ 405.00