Consolidated cash flow statements (Parenthetical) - USD ($) $ in Millions |
12 Months Ended | |
|---|---|---|
Dec. 31, 2018 |
Dec. 31, 2017 |
|
| Consolidated cash flow statements [Abstract] | ||
| Proceeds from investments in contracted concessional assets | $ 72.6 | $ 42.5 |
| Purchase of investments in contracted concessional assets | $ 4.6 | $ 12.4 |