Condensed Consolidated Balance Sheets (Unaudited) (USD $) In Millions	Jun. 30, 2011	Dec. 31, 2010	Jun. 30, 2010
Current assets
Cash and cash equivalents	$ 42.9	$ 31.5	$ 59.8
Short-term investments	52.7	70.6	66.6
Receivables, less allowances of $41.7, $27.6 and $50.1, respectively	289.4	472.4	268.1
Gas in storage	59.2	163.9	53.4
Derivative instruments	36.6	49.1	44.4
Margin accounts - derivative instruments	33.8	50.9	52.6
Other	111.9	115.2	111.9
Total current assets	626.5	953.6	656.8
Property, plant and equipment, at cost [Abstract]
Property, plant and equipment, at cost	5,210.0	5,127.7	5,029.4
Less accumulated depreciation	2,150.1	2,104.9	2,069.4
Total property, plant and equipment, net	3,059.9	3,022.8	2,960.0
Long-term investments	133.9	134.2	137.0
Other assets	387.8	385.9	373.7
Total assets	4,208.1	4,496.5	4,127.5
Current liabilities
Long-term debt due within one year	0	0	75.0
Short-term debt	66.0	425.0	107.0
Accounts payable	313.5	335.5	293.9
Customer credit balances and deposits	83.7	110.6	101.5
Temporary LIFO inventory liquidation	88.6	0	87.7
Derivative instruments	57.3	82.9	88.1
Other	111.5	120.3	107.8
Total current liabilities	720.6	1,074.3	861.0
Deferred credits and other liabilities
Regulatory asset retirement liability	866.9	843.9	825.7
Deferred income taxes	433.9	423.4	405.3
Health care and other postretirement benefits	231.5	229.7	201.0
Asset retirement obligation	195.2	190.9	186.5
Other	137.8	132.0	136.5
Total deferred credits and other liabilities	1,865.3	1,819.9	1,755.0
Commitments and contingencies
Capitalization
Long-term obligations	498.5	498.4	423.4
Common equity
Common stock	113.9	113.9	113.8
Paid-in capital	67.8	69.1	65.6
Retained earnings	955.6	934.1	923.1
Accumulated other comprehensive loss	(13.6)	(13.2)	(14.4)
Total common equity	1,123.7	1,103.9	1,088.1
Total capitalization	1,622.2	1,602.3	1,511.5
Total liabilities and capitalization	4,208.1	4,496.5	4,127.5
Gas Distribution [Member]
Property, plant and equipment, at cost [Abstract]
Property, plant and equipment, at cost	4,795.3	4,733.6	4,646.1
Shipping [Member]
Property, plant and equipment, at cost [Abstract]
Property, plant and equipment, at cost	325.6	333.6	338.4
Other [Member]
Property, plant and equipment, at cost [Abstract]
Property, plant and equipment, at cost	$ 89.1	$ 60.5	$ 44.9