STATEMENTS OF SHAREHOLDERS' EQUITY (UNAUDITED) (Parenthetical) - $ / shares	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Class A common stock
Dividends declared (in dollars per share)	$ 0.90	$ 0.90	$ 0.90	$ 0.84	$ 0.84	$ 0.84	$ 2.70	$ 2.52
Class B common stock
Dividends declared (in dollars per share)	$ 135.00	$ 135.00	$ 135.00	$ 126.00	$ 126.00	$ 126.00	$ 405.00	$ 378.00