Stock-Based Compensation Plans (Restricted Stock Units) (Details) - $ / shares shares in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2017	Sep. 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		$ 26.19
Forfeited, shares		0.0
Forfeited, weighted average fair value at date of grant		$ 0.00
Non-vested, ending balance, shares	0.3	0.3
Non-vested, ending balance, weighted average fair value at date of grant	$ 21.28	$ 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	0.4	0.6	0.5
Granted, weighted average fair value at date of grant	$ 23.81	$ 23.59	$ 26.53
Vested, shares		(0.5)
Vested, weighted average fair value at date of grant		$ 22.81
Forfeited, shares		0.0
Forfeited, weighted average fair value at date of grant		$ 0.00
Non-vested, ending balance, shares	1.4	1.4
Non-vested, ending balance, weighted average fair value at date of grant	$ 23.49	$ 23.49