Earnings Per Common Share (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Numerator (basic and diluted):
Income from continuing operations	$ 134	$ 111	$ 393	$ 281
Less: Allocation to unvested restricted stock awards	2	2	5	4
Income from continuing operations attributable to common shareholders	132	109	388	277
Loss from discontinued operations, net	0	0	0	(1)
Less: Allocation to unvested restricted stock awards	0	0	0	0
Loss from discontinued operations attributable to common shareholders	0	0	0	(1)
Net income available to common shareholders	$ 132	$ 109	$ 388	$ 276
Denominator:
Basic common shares (based upon weighted average) (in shares)	326	335	328	340
Add: Stock option dilution (in shares)	3	3	4	4
Diluted common shares (in shares)	329	338	332	344