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		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Earnings Per Share [Abstract]
Income from continuing operations	$ 63	$ 92	$ 137	$ 130
Less: Noncontrolling interests	$ 4	4	$ 15	7
Less: Preferred stock dividend requirements		2		5
Income from continuing operations available to common stockholders - Numerator basic	$ 59	86	$ 122	118
Numerator diluted	59	88	122	123
Net income available to common stockholders	59	84	122	115
Numerator diluted	$ 59	$ 86	$ 122	$ 120
Weighted-average number of shares outstanding - Denominator basic	162.1	156.7	163.4	153.7
Employee compensation-related shares, including stock options	1.1	1.3	1.2	1.2
Conversion of preferred stock		17.1		21.1
Denominator diluted	163.2	175.1	164.6	176.0