Note 5 - Derivative Instruments (Details) - Derivative Instruments on the Consolidated Statements of Income - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Designated as cash flow or fair value hedges
Income tax benefit			$ (1)		$ (1)
Total designated as cash flow or fair value hedges, net of tax		$ (4)	1	$ (4)	5
Not designated as hedges (1)
Total gains (losses) on derivative instruments, net of tax		(1)	19	(17)	6
Cash Flow Hedging [Member]
Designated as cash flow or fair value hedges
Income tax benefit			(1)		(1)
Total designated as cash flow or fair value hedges, net of tax		(4)	1	(4)	$ 5
Fair Value Hedging [Member]
Not designated as hedges (1)
Income tax benefit	[1]	(1)	(11)	9
Total not designated as hedges, net of tax	[1]	3	18	(13)	$ 1
Cost of Sales [Member] | Cash Flow Hedging [Member]
Designated as cash flow or fair value hedges
Natural gas contracts - gain reclassified from OCI		(3)	2	(4)	5
Cost of Sales [Member] | Fair Value Hedging [Member]
Not designated as hedges (1)
Natural gas contracts - net value adjustments	[1],[2]	1	(1)	(1)	1
Operating Expense [Member] | Cash Flow Hedging [Member]
Designated as cash flow or fair value hedges
Natural gas contracts - gain reclassified from OCI		(1)		(1)	$ 1
Interest Expense [Member] | Cash Flow Hedging [Member]
Designated as cash flow or fair value hedges
Interest rate swaps - net loss reclassified from OCI into interest expense				1
Sales [Member] | Fair Value Hedging [Member]
Not designated as hedges (1)
Natural gas contracts - net value adjustments	[1]	$ 3	$ 30	$ (21)

[1] Associated with the fair value of derivative instruments held at June 30, 2015 and 2014.

[2] Excludes (gains) losses recorded in cost of goods sold associated with weather derivatives of $(1) million and $1 million for the three and six months ended June30, 2015 and $1 million and $6 million for the three and six months ended June 30, 2014.