Regulatory Matters (Tables)
 12 Months Ended
Dec. 31, 2015
Regulatory Assets and Liabilities Disclosure [Abstract]  
Regulatory Assets
At December 31, (in millions)
2015
 
2014
 
 
 
Predecessor
Assets
 
 
 
Unrecognized pension benefit and other postretirement benefit costs
$
127.1

 
$
120.9

Other postretirement costs
8.9

 
10.8

Deferred taxes on AFUDC equity
—

 
21.8

Other
3.1

 
4.5

Total Regulatory Assets
$
139.1

 
$
158.0
Regulatory Liabilities
At December 31, (in millions)
2015
 
2014
 
 
 
Predecessor
Liabilities
 
 
 
Cost of removal
$
153.5

 
$
156.2

Regulatory effects of accounting for income taxes
—

 
10.9

Unrecognized pension benefit and other postretirement benefit costs
0.6

 
8.3

Other postretirement costs
155.6

 
117.3

Other
1.2

 
2.9

Total Regulatory Liabilities
$
310.9

 
$
295.6