Transactions With Affiliates (Schedule of Affiliated Transactions) (Details) - USD ($) $ in Millions |
3 Months Ended | ||
|---|---|---|---|
Mar. 31, 2016 |
Mar. 31, 2015 |
Dec. 31, 2015 |
|
| Related Party Transaction [Line Items] | |||
| Transportation revenues | $ 0.0 | $ 28.7 | |
| Storage revenues | 0.0 | 13.3 | |
| Other revenues | 0.0 | 0.1 | |
| Operation and maintenance | 42.4 | 36.1 | |
| Interest expense | 7.2 | 11.4 | |
| Interest income | 0.1 | $ 1.0 | |
| Accounts receivable | 122.6 | $ 149.4 | |
| Short-term borrowings | 348.8 | 42.1 | |
| Accounts payable | 22.6 | 86.3 | |
| Long-term debt | $ 630.9 | $ 630.9 | |