Earnings Per Share - Reconciliation of the Numerators and Denominators of the Earnings Per Share Calculations (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Earnings Per Share [Abstract]
Income from continuing operations	$ 122	$ 94	$ 259	$ 224
Less: Noncontrolling interests	$ 3	3	$ 18	10
Less: Preferred stock dividend requirements		2		7
Income from continuing operations available to common stockholders - Numerator basic	$ 119	89	$ 241	207
Numerator diluted	119	91	241	214
Net income available to common stockholders	119	88	241	203
Numerator diluted	$ 119	$ 90	$ 241	$ 210
Weighted-average number of shares outstanding - Denominator basic	158.0	156.5	161.6	154.6
Employee compensation-related shares, including stock options	0.9	1.3	1.1	1.2
Conversion of preferred stock		15.1		19.1
Denominator diluted	158.9	172.9	162.7	174.9