Earnings Per Common Share (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Numerator (basic and diluted):
Income from continuing operations	$ 150	$ 109	$ 259	$ 170
Less: Allocation to unvested restricted stock awards	2	1	3	2
Income from continuing operations attributable to common shareholders	148	108	256	168
Loss from discontinued operations, net	0	(4)	0	(1)
Less: Allocation to unvested restricted stock awards	0	0	0	0
Loss from discontinued operations attributable to common shareholders	0	(4)	0	(1)
Net income available to common shareholders	$ 148	$ 104	$ 256	$ 167
Denominator:
Basic common shares (based upon weighted average) (in shares)	328	340	329	342
Add: Stock option dilution (in shares)	3	4	4	4
Diluted common shares (in shares)	331	344	333	346