Note 3 - Merger with Nicor (Detail) - Purchase Price Allocation of Regulatory Assets and Liabilities (USD $) In Millions, unless otherwise specified	Mar. 31, 2012
Current assets	$ 932
Other noncurrent assets, excluding goodwill	791
Current liabilities	(1,170)
Other noncurrent liabilities	(2,048)
Regulatory Assets [Member]
Current assets	36
Other noncurrent assets, excluding goodwill	477
Regulatory Liabilities [Member]
Current liabilities	(80)
Other noncurrent liabilities	$ (1,137)