Note 2 - Significant Accounting Policies and Methods of Application (Detail) - Summary of Regulatory Assets and Liabilities (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
Regulatory assets
Regulatory assets - current	$ 119	$ 145	$ 137
Regulatory assets - noncurrent	878	944	1,057
Total regulatory assets	997	1,089	1,194
Regulatory liabilities
Regulatory liabilities - current	238	161	173
Regulatory liabilities - noncurrent	1,498	1,477	1,431
Total regulatory liabilities	1,736	1,638	1,604
Accrued natural gas costs [Member]
Regulatory liabilities
Regulatory liabilities - current	133	93	97
Bad debt rider [Member]
Regulatory liabilities
Regulatory liabilities - current	39	37	32
Regulatory liabilities - noncurrent	20	17	20
Accumulated removal costs [Member]
Regulatory liabilities
Regulatory liabilities - current	17	16	14
Regulatory liabilities - noncurrent	1,413	1,393	1,339
Other Regulatory Liabilities [Member]
Regulatory liabilities
Regulatory liabilities - current	49	15	30
Regulatory liabilities - noncurrent	11	11	14
Unamortized investment tax credit [Member]
Regulatory liabilities
Regulatory liabilities - noncurrent	28	29	32
Regulatory income tax liability [Member]
Regulatory liabilities
Regulatory liabilities - noncurrent	26	27	26
Recoverable regulatory infrastructure program costs [Member]
Regulatory assets
Regulatory assets - current	47	47	48
Regulatory assets - noncurrent	135	167	291
Recoverable Environmental Remediation Costs [Member]
Regulatory assets
Regulatory assets - current	28	38	7
Regulatory assets - noncurrent	415	438	349
Recoverable Pension And Other Retirement Benefit Costs [Member]
Regulatory assets
Regulatory assets - current	19	19	29
Regulatory assets - noncurrent	192	196	256
Other Regulatory Assets [Member]
Regulatory assets
Regulatory assets - current	25	41	53
Regulatory assets - noncurrent	48	53	64
Long-Term Debt Fair Value Adjustment [Member]
Regulatory assets
Regulatory assets - noncurrent	$ 88	$ 90	$ 97