Share-Based Compensation Plans - Stock activity - RSUs, PSUs, MSUs (Details) (USD $)	12 Months Ended	6 Months Ended		12 Months Ended
	Dec. 31, 2014	Dec. 31, 2014	Jul. 11, 2014	Dec. 31, 2012
Nonvested share activity [Rollforward]
Options Exercised - shares	(18,300)
Weighted-average grant-date fair value [Rollforward]
Options Exercised - Exercise Price	$ 20.34
Performance Shares PSU [Member]
Nonvested share activity [Rollforward]
Nonvested beginning balance	199,300	384,400	199,300
Granted		1,500	187,800
Cancelled		(42,300)	(2,700)
Nonvested ending balance	343,600	343,600	384,400
Weighted-average grant-date fair value [Rollforward]
Nonvested beginning balance		$ 24.06
Granted		$ 24.41
Cancelled		$ 24.02
Nonvested ending balance	$ 24.06	$ 24.06	$ 24.06
Fair Value at Issuance Data [Abstract]
Nonvested beginning balance	$ 26.22	$ 28.39	$ 26.22
Granted			$ 30.67
Cancelled			$ 26.46
Nonvested ending balance			$ 28.39
Restricted Stock Units [Member]
Nonvested share activity [Rollforward]
Nonvested beginning balance	396,400	384,700	396,400
Granted		45,000	136,700
Cancelled		(50,000)	(5,600)
Vested		(12,600)	(142,800)
Nonvested ending balance	367,100	367,100	384,700
Weighted-average grant-date fair value [Rollforward]
Nonvested beginning balance		$ 26.47
Granted		$ 21.67
Cancelled		$ 26.37
Vested		$ 26.93
Nonvested ending balance	$ 25.87	$ 25.87	$ 26.47
Fair Value at Issuance Data [Abstract]
Nonvested beginning balance	$ 24.58	$ 26.18	$ 24.58
Granted			$ 29.97
Cancelled			$ 24.75
Vested			$ 25.44
Nonvested ending balance			$ 26.18
Market Share Units MSU [Member]
Nonvested share activity [Rollforward]
Nonvested beginning balance	96,200	179,100	96,200
Granted			82,900
Cancelled		(15,800)
Nonvested ending balance	163,300	163,300	179,100
Weighted-average grant-date fair value [Rollforward]
Nonvested beginning balance		$ 25.47
Cancelled		$ 25.47
Nonvested ending balance	$ 25.47	$ 25.47	$ 25.47
Fair Value at Issuance Data [Abstract]
Nonvested beginning balance	$ 26.42	$ 28.48	$ 26.42
Granted			$ 30.87
Nonvested ending balance			$ 28.48
Stock Options [Member]
Nonvested share activity [Rollforward]
Nonvested beginning balance	1,474,900	871,700	1,474,900
Cancelled		(18,500)	(593,300)
Options Exercised - shares		(8,400)	(9,900)
Nonvested ending balance	844,800	844,800	871,700
Weighted-average grant-date fair value [Rollforward]
Nonvested beginning balance		$ 5.74
Granted			$ 7.78	$ 6.32
Cancelled		$ 6.18
Options Exercised - Exercise Price		$ 7.77
Nonvested ending balance	$ 5.83	$ 5.83	$ 5.74
Fair Value at Issuance Data [Abstract]
Nonvested beginning balance	$ 7.68	$ 7.33	$ 7.68
Cancelled			$ 8.22
Excercised, Fair Value Issuance Date			$ 5.69
Nonvested ending balance			$ 7.33
Deferred Stock Units [Member]
Nonvested share activity [Rollforward]
Nonvested beginning balance	19,200		19,200
Granted	28,300
Vested	(19,200)
Nonvested ending balance	28,300	28,300
Weighted-average grant-date fair value [Rollforward]
Nonvested beginning balance	$ 26.8		$ 26.8
Granted	$ 24.7
Vested	$ 26.8
Nonvested ending balance	$ 24.7	$ 24.7		$ 22.35