Supplemental Equity and Comprehensive Income Information (Details 7) (USD $)	1 Months Ended		3 Months Ended				12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Supplemental Equity and Comprehensive Income Information
Dividends that have been declared but not yet paid (in dollars per share)	$ 1.025	$ 0.855
Dividends declared in current period (in dollars per share)			$ 0.855	$ 0.855	$ 0.855		$ 3.59	$ 3.395	$ 2.36
Dividends paid in current period (in dollars per share)						$ 0.855	$ 3.42	$ 2.54	$ 2.36