Note 2 - Significant Accounting Policies and Methods of Application (Details) - Summary of Regulatory Assets and Liabilities (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
Regulatory assets
Regulatory assets - current	$ 133	$ 145	$ 158
Regulatory assets - noncurrent	871	944	994
Total regulatory assets	1,004	1,089	1,152
Regulatory liabilities
Regulatory liabilities - current	174	161	117
Regulatory liabilities - noncurrent	1,524	1,477	1,465
Total regulatory liabilities	1,698	1,638	1,582
Accrued natural gas costs [Member]
Regulatory liabilities
Regulatory liabilities - current	104	93	62
Bad debt rider [Member]
Regulatory liabilities
Regulatory liabilities - current	37	37	30
Regulatory liabilities - noncurrent	20	17	16
Accumulated removal costs [Member]
Regulatory liabilities
Regulatory liabilities - current	17	16	14
Regulatory liabilities - noncurrent	1,448	1,393	1,381
Other Regulatory Liabilities [Member]
Regulatory liabilities
Regulatory liabilities - current	16	15	11
Regulatory liabilities - noncurrent	4	11	15
Unamortized investment tax credit [Member]
Regulatory liabilities
Regulatory liabilities - noncurrent	26	29	30
Regulatory income tax liability [Member]
Regulatory liabilities
Regulatory liabilities - noncurrent	26	27	23
Recoverable regulatory infrastructure program costs [Member]
Regulatory assets
Regulatory assets - current	46	47	46
Regulatory assets - noncurrent	104	167	194
Recoverable Environmental Remediation Costs [Member]
Regulatory assets
Regulatory assets - current	30	38	33
Regulatory assets - noncurrent	456	438	421
Recoverable Pension And Other Retirement Benefit Costs [Member]
Regulatory assets
Regulatory assets - current	19	19	27
Regulatory assets - noncurrent	183	196	228
Other Regulatory Assets [Member]
Regulatory assets
Regulatory assets - current	38	41	52
Regulatory assets - noncurrent	44	53	59
Long-Term Debt Fair Value Adjustment [Member]
Regulatory assets
Regulatory assets - noncurrent	$ 84	$ 90	$ 92