STATEMENTS OF SHAREHOLDERS' EQUITY (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Class A
Dividends declared (in dollars per share)	$ 3.1875	$ 2.9725	$ 2.773
Class B
Dividends declared (in dollars per share)	$ 478.125	$ 445.875	$ 415.95