Share-based compensation plans - Stock activity - RSU, PSU, MSU, DSU (Details) - $ / shares
|
9 Months Ended |
12 Months Ended |
Sep. 30, 2018 |
Dec. 31, 2017 |
| Restricted Stock Units |
|
|
| Shares (in thousands) |
|
|
| Nonvested, beginning balance, shares |
265,800
|
|
| Granted, shares |
83,500
|
|
| Forfeited, shares |
(3,800)
|
|
| Vested, shares |
(95,800)
|
|
| Nonvested, ending balance, shares |
249,700
|
265,800
|
| Weighted-Average Grant Date Fair Value Per Share |
|
|
| Nonvested, beginning balance (dollars per share) |
$ 39.80
|
|
| Granted (dollars per share) |
72.51
|
|
| Forfeited (dollars per share) |
56.52
|
|
| Vested (dollars per share) |
35.71
|
|
| Nonvested, ending balance (dollars per share) |
$ 52.06
|
$ 39.80
|
| Performance Shares Units PSU |
|
|
| Shares (in thousands) |
|
|
| Nonvested, beginning balance, shares |
671,200
|
|
| Granted, shares |
174,400
|
|
| Forfeited, shares |
(5,800)
|
|
| Vested, shares |
(137,700)
|
|
| Nonvested, ending balance, shares |
702,100
|
671,200
|
| Weighted-Average Grant Date Fair Value Per Share |
|
|
| Nonvested, beginning balance (dollars per share) |
$ 37.26
|
|
| Granted (dollars per share) |
73.61
|
|
| Forfeited (dollars per share) |
50.63
|
|
| Vested (dollars per share) |
29.17
|
|
| Nonvested, ending balance (dollars per share) |
$ 47.75
|
$ 37.26
|
| Actual shares earned and distributed (shares) |
|
344,300,000
|
| Market Share Units MSU |
|
|
| Shares (in thousands) |
|
|
| Nonvested, beginning balance, shares |
74,200
|
|
| Granted, shares |
0
|
|
| Forfeited, shares |
0
|
|
| Vested, shares |
(74,200)
|
|
| Nonvested, ending balance, shares |
0
|
74,200
|
| Weighted-Average Grant Date Fair Value Per Share |
|
|
| Nonvested, beginning balance (dollars per share) |
$ 30.37
|
|
| Granted (dollars per share) |
0.00
|
|
| Forfeited (dollars per share) |
0.00
|
|
| Vested (dollars per share) |
30.37
|
|
| Nonvested, ending balance (dollars per share) |
$ 0.00
|
$ 30.37
|
| Actual shares earned and distributed (shares) |
|
111,300,000
|
| Deferred Stock Units |
|
|
| Shares (in thousands) |
|
|
| Nonvested, beginning balance, shares |
10,900
|
|
| Granted, shares |
12,500
|
|
| Forfeited, shares |
0
|
|
| Vested, shares |
(10,900)
|
|
| Nonvested, ending balance, shares |
12,500
|
10,900
|
| Weighted-Average Grant Date Fair Value Per Share |
|
|
| Nonvested, beginning balance (dollars per share) |
$ 60.80
|
|
| Granted (dollars per share) |
74.43
|
|
| Forfeited (dollars per share) |
0.00
|
|
| Vested (dollars per share) |
60.80
|
|
| Nonvested, ending balance (dollars per share) |
$ 74.43
|
$ 60.80
|