Consolidated Statement of Changes in Common Shareholders' Equity (Parenthetical) - $ / shares	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Statement of Stockholders' Equity [Abstract]
Dividends on common stock per share (in dollars per share)	$ 0.40	$ 0.40	$ 0.80	$ 0.7625