Equity-Indexed Compensation Plans (Details) - 6 months ended Jun. 30, 2015 - Long-Term Incentive Plan Awards - $ / shares shares in Millions	Total
Outstanding (in units)
Outstanding at beginning of period (in units)	7.3
Granted (in units)	1.1
Vested (in units)	(1.8)
Cancelled or forfeited (in units)	(0.1)
Outstanding at end of period (in units)	6.5
Weighted Average Grant Date Fair Value per Unit
Outstanding at beginning of period (in dollars per unit)	$ 41.45
Granted (in dollars per unit)	39.98
Vested (in dollars per unit)	25.96
Cancelled or forfeited (in dollars per unit)	43.26
Outstanding at end of period (in dollars per unit)	$ 45.47
Units issued in connection with the settlement of vested awards, net of tax withholding (in units)	0.5
Units withheld for taxes (in units)	0.2
Vested awards settled in cash (in units)	1.1