Share-based compensation plans - Stock activity - RSUs, PSUs, MSUs(Details) - $ / shares
|
3 Months Ended |
12 Months Ended |
Mar. 31, 2017 |
Mar. 31, 2016 |
Dec. 31, 2016 |
| Restricted Stock |
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] |
|
|
|
| Nonvested, beginning balance, shares |
296,500
|
|
|
| Granted, shares |
91,700
|
|
|
| Forfeited, shares |
(10,800)
|
|
|
| Vested, shares |
(88,600)
|
|
|
| Nonvested, ending balance, shares |
288,800
|
|
296,500
|
| Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract] |
|
|
|
| Nonvested, beginning balance (dollars per share) |
$ 27.84
|
|
|
| Granted (dollars per share) |
51.96
|
|
|
| Forfeited (dollars per share) |
27.31
|
|
|
| Vested (dollars per share) |
27.47
|
|
|
| Nonvested, ending balance (dollars per share) |
$ 35.63
|
|
$ 27.84
|
| Performance Shares |
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] |
|
|
|
| Nonvested, beginning balance, shares |
603,200
|
|
|
| Granted, shares |
214,100
|
|
|
| Forfeited, shares |
(12,100)
|
|
|
| Vested, shares |
(134,300)
|
|
|
| Nonvested, ending balance, shares |
670,900
|
|
603,200
|
| Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract] |
|
|
|
| Nonvested, beginning balance (dollars per share) |
$ 28.02
|
|
|
| Granted (dollars per share) |
53.66
|
|
|
| Forfeited (dollars per share) |
27.53
|
|
|
| Vested (dollars per share) |
24.39
|
|
|
| Nonvested, ending balance (dollars per share) |
$ 36.94
|
|
$ 28.02
|
| Number of shares earned and distributed |
|
252,000,000
|
|
| Market Share Units MSU |
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] |
|
|
|
| Nonvested, beginning balance, shares |
141,700
|
|
|
| Granted, shares |
0
|
|
|
| Forfeited, shares |
0
|
|
|
| Vested, shares |
(67,500)
|
|
|
| Nonvested, ending balance, shares |
74,200
|
|
141,700
|
| Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract] |
|
|
|
| Nonvested, beginning balance (dollars per share) |
$ 27.02
|
|
|
| Granted (dollars per share) |
0.00
|
|
|
| Forfeited (dollars per share) |
0.00
|
|
|
| Vested (dollars per share) |
23.34
|
|
|
| Nonvested, ending balance (dollars per share) |
$ 30.37
|
|
$ 27.02
|
| Number of shares earned and distributed |
|
|
81,800,000
|