|
Accumulated Other Comprehensive Income (Details) (USD $)
In Millions, unless otherwise specified
|
3 Months Ended |
12 Months Ended |
|
Mar. 31, 2015
|
Mar. 31, 2014
|
Mar. 31, 2015
|
Mar. 31, 2014
|
| Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract] |
|
|
|
|
|
|
|
|
| AOCI at beginning of period |
$ (201.3) |
|
$ (141.8) |
|
$ (139.1) |
|
$ (241.3) |
|
| OCI before reclassifications |
|
|
|
|
(113.6) |
|
135.7 |
|
| Reclassified from AOCI |
6.2 |
[1] |
4.5 |
[1] |
18.9 |
[1] |
30.0 |
[1] |
| Income taxes |
|
|
|
|
|
|
|
|
| Attributable to OCI before reclassifications |
|
|
|
|
43.4 |
|
(51.8) |
|
| Attributable to amounts reclassified from AOCI |
(2.4) |
[2] |
(1.8) |
[2] |
(7.1) |
[2] |
(11.7) |
[2] |
| Total income taxes |
2.4 |
|
1.8 |
|
(36.3) |
|
63.5 |
|
| Net other comprehensive income (loss) |
3.8 |
|
2.7 |
|
(58.4) |
|
102.2 |
|
| AOCI at end of period |
(197.5) |
|
(139.1) |
|
(197.5) |
|
(139.1) |
|
| Reclassification Adjustment out of Accumulated Other Comphrensive Income [Abstract] |
|
|
|
|
|
|
|
|
| Income tax benefit |
(48.8) |
|
(50.1) |
|
(124.6) |
|
(103.5) |
|
| Pension and OPRB |
|
|
|
|
|
|
|
|
| Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract] |
|
|
|
|
|
|
|
|
| AOCI at beginning of period |
(178.9) |
|
(119.0) |
|
(116.4) |
|
(218.3) |
|
| OCI before reclassifications |
|
|
|
|
(113.6) |
|
135.8 |
|
| Reclassified from AOCI |
6.0 |
[1] |
4.3 |
[1] |
18.4 |
[1] |
29.5 |
[1] |
| Income taxes |
|
|
|
|
|
|
|
|
| Attributable to OCI before reclassifications |
|
|
|
|
43.4 |
|
(51.9) |
|
| Attributable to amounts reclassified from AOCI |
(2.3) |
[2] |
(1.7) |
[2] |
(7.0) |
[2] |
(11.5) |
[2] |
| Total income taxes |
|
|
|
|
(36.4) |
|
63.4 |
|
| Net other comprehensive income (loss) |
3.7 |
|
2.6 |
|
(58.8) |
|
101.9 |
|
| AOCI at end of period |
(175.2) |
|
(116.4) |
|
(175.2) |
|
(116.4) |
|
| Long-term invest. |
|
|
|
|
|
|
|
|
| Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract] |
|
|
|
|
|
|
|
|
| AOCI at beginning of period |
0.1 |
|
0.1 |
|
0.1 |
|
0.1 |
|
| OCI before reclassifications |
|
|
|
|
0 |
|
(0.1) |
|
| Reclassified from AOCI |
0 |
[1] |
0 |
[1] |
0 |
[1] |
0 |
[1] |
| Income taxes |
|
|
|
|
|
|
|
|
| Attributable to OCI before reclassifications |
|
|
|
|
0 |
|
0.1 |
|
| Attributable to amounts reclassified from AOCI |
0 |
[2] |
0 |
[2] |
0 |
[2] |
0 |
[2] |
| Total income taxes |
|
|
|
|
0 |
|
(0.1) |
|
| Net other comprehensive income (loss) |
0 |
|
0 |
|
0 |
|
0 |
|
| AOCI at end of period |
0.1 |
|
0.1 |
|
0.1 |
|
0.1 |
|
| Questar Pipeline [Member] |
|
|
|
|
|
|
|
|
| Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract] |
|
|
|
|
|
|
|
|
| AOCI at beginning of period |
(22.5) |
|
|
|
(22.8) |
|
|
|
| Income taxes |
|
|
|
|
|
|
|
|
| Total income taxes |
0.1 |
|
0.1 |
|
0.1 |
|
0.2 |
|
| Net other comprehensive income (loss) |
0.1 |
|
0.1 |
|
0.4 |
|
0.3 |
|
| AOCI at end of period |
(22.4) |
|
(22.8) |
|
(22.4) |
|
(22.8) |
|
| Reclassification Adjustment out of Accumulated Other Comphrensive Income [Abstract] |
|
|
|
|
|
|
|
|
| Income tax benefit |
(8.0) |
|
(9.1) |
|
(34.5) |
|
(7.0) |
|
| Questar Pipeline [Member] | Interest rate cash flow hedges |
|
|
|
|
|
|
|
|
| Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract] |
|
|
|
|
|
|
|
|
| AOCI at beginning of period |
(22.5) |
|
(22.9) |
|
(22.8) |
|
(23.1) |
|
| OCI before reclassifications |
|
|
|
|
0 |
|
0 |
|
| Reclassified from AOCI |
0.2 |
[1] |
0.2 |
[1] |
0.5 |
[1] |
0.5 |
[1] |
| Income taxes |
|
|
|
|
|
|
|
|
| Attributable to OCI before reclassifications |
|
|
|
|
0 |
|
0 |
|
| Attributable to amounts reclassified from AOCI |
(0.1) |
[2] |
(0.1) |
[2] |
(0.1) |
[2] |
(0.2) |
[2] |
| Total income taxes |
|
|
|
|
0.1 |
|
0.2 |
|
| Net other comprehensive income (loss) |
0.1 |
|
0.1 |
|
0.4 |
|
0.3 |
|
| AOCI at end of period |
(22.4) |
|
(22.8) |
|
(22.4) |
|
(22.8) |
|
| Questar Pipeline [Member] | Interest rate cash flow hedges | Reclassification out of Accumulated Other Comprehensive Income [Member] |
|
|
|
|
|
|
|
|
| Reclassification Adjustment out of Accumulated Other Comphrensive Income [Abstract] |
|
|
|
|
|
|
|
|
| Interest (expense) |
(0.2) |
|
(0.2) |
|
(0.5) |
|
(0.5) |
|
| Income tax benefit |
$ 0.1 |
|
$ 0.1 |
|
$ 0.1 |
|
$ 0.2 |
|
|
|
|