Note 2 - Significant Accounting Policies and Methods of Application (Details) - Summary of Regulatory Assets and Liabilities (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012
Regulatory assets
Regulatory assets - current	$ 120	$ 145	$ 146
Regulatory assets - noncurrent	898	944	1,083
Total regulatory assets	1,018	1,089	1,229
Regulatory liabilities
Regulatory liabilities - current	216	161	137
Regulatory liabilities - noncurrent	1,510	1,477	1,453
Total regulatory liabilities	1,726	1,638	1,590
Accrued natural gas costs [Member]
Regulatory liabilities
Regulatory liabilities - current	130	93	73
Bad debt rider [Member]
Regulatory liabilities
Regulatory liabilities - current	39	37	31
Regulatory liabilities - noncurrent	20	17	18
Accumulated removal costs [Member]
Regulatory liabilities
Regulatory liabilities - current	17	16	14
Regulatory liabilities - noncurrent	1,431	1,393	1,366
Other Regulatory Liabilities [Member]
Regulatory liabilities
Regulatory liabilities - current	30	15	19
Regulatory liabilities - noncurrent	6	11	13
Unamortized investment tax credit [Member]
Regulatory liabilities
Regulatory liabilities - noncurrent	27	29	31
Regulatory income tax liability [Member]
Regulatory liabilities
Regulatory liabilities - noncurrent	26	27	25
Recoverable regulatory infrastructure program costs [Member]
Regulatory assets
Regulatory assets - current	46	47	47
Regulatory assets - noncurrent	116	167	268
Recoverable Environmental Remediation Costs [Member]
Regulatory assets
Regulatory assets - current	27	38	30
Regulatory assets - noncurrent	458	438	428
Recoverable Pension And Other Retirement Benefit Costs [Member]
Regulatory assets
Regulatory assets - current	19	19	27
Regulatory assets - noncurrent	188	196	232
Other Regulatory Assets [Member]
Regulatory assets
Regulatory assets - current	28	41	42
Regulatory assets - noncurrent	50	53	61
Long-Term Debt Fair Value Adjustment [Member]
Regulatory assets
Regulatory assets - noncurrent	$ 86	$ 90	$ 94