Stock-Based Compensation Plans (Restricted Stock Units) (Details) - $ / shares shares in Millions	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
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	$ 26.48
Granted, shares	0.3
Granted, weighted average fair value at date of grant	$ 21.27
Vested, shares	(0.3)
Vested, weighted average fair value at date of grant	$ 26.23
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	$ 21.28
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	$ 23.23
Granted, shares	0.2	0.5
Granted, weighted average fair value at date of grant	$ 23.06	$ 26.43
Vested, shares	(0.5)
Vested, weighted average fair value at date of grant	$ 22.72
Forfeited, shares	0.0
Forfeited, weighted average fair value at date of grant	$ 0.00
Non-vested, ending balance, shares	1.0
Non-vested, ending balance, weighted average fair value at date of grant	$ 23.38