Stock-Based Compensation Plans (Restricted Stock Units) (Details) - $ / shares shares in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Performance Shares [Member]
Changes to non-vested restricted stock and restricted stock units
Non-vested, beginning balance, shares	0.3
Non-vested, beginning balance, weighted average fair value at date of grant	$ 21.84
Granted, shares	0.3
Granted, weighted average fair value at date of grant	$ 26.49
Vested, shares	(0.3)
Vested, weighted average fair value at date of grant	$ 21.84
Forfeited, shares	0.0
Forfeited, weighted average fair value at date of grant	$ 0.00
Non-vested, ending balance, shares	0.3
Non-vested, ending balance, weighted average fair value at date of grant	$ 26.45
Time-Based Restricted Stock [Member]
Changes to non-vested restricted stock and restricted stock units
Non-vested, beginning balance, shares	1.3
Non-vested, beginning balance, weighted average fair value at date of grant	$ 20.20
Granted, shares	0.5	0.7
Granted, weighted average fair value at date of grant	$ 26.34	$ 22.10
Vested, shares	(0.4)
Vested, weighted average fair value at date of grant	$ 18.97
Forfeited, shares	0.0
Forfeited, weighted average fair value at date of grant	$ 0.00
Non-vested, ending balance, shares	1.4
Non-vested, ending balance, weighted average fair value at date of grant	$ 22.84