Earnings Per Common Share (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Numerator (basic and diluted):
Income from continuing operations	$ 109	$ 124	$ 170	$ 202
Less: Allocation to unvested restricted stock awards	1	2	2	4
Income from continuing operations attributable to common shareholders	108	122	168	198
(Loss) gain from discontinued operations, net	(4)	15	(1)	11
(Loss) gain from discontinued operations attributable to common shareholders	(4)	15	(1)	11
Net income available to common shareholders	$ 104	$ 137	$ 167	$ 209
Denominator:
Basic common shares (based upon weighted average) (in shares)	340	349	342	350
Add: Stock option dilution (in shares)	4	3	4	3
Diluted common shares (in shares)	344	352	346	353