Note 6 - Employee Benefit Plans (Details) - Employee Benefit Plans (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Long-term asset (2)	$ 97		$ 117
Defined Benefit Plan Change In Fair Value Of Plan Assets [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, January 1,	907		837
Actual return on plan assets	68		134
Employer contributions	1		1
Benefits paid	(70)		(65)
Fair value of plan assets, December 31,	906		907
Defined Benefit Plan Change In Fair Value Of Plan Assets [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, January 1,	93		77
Actual return on plan assets	5		16
Employee contributions	2		3
Employer contributions	17		19
Benefits paid	(19)		(23)
Medicare Part D reimbursements	1		1
Fair value of plan assets, December 31,	99		93
Defined Benefit Plan Change In Benefit Obligation [Member] | Pension Plan [Member] | Long-term Asset [Member]
Defined Benefit Plan Disclosure [Line Items]
Long-term asset (2)	97	[1]	117	[1]
Defined Benefit Plan Change In Benefit Obligation [Member] | Pension Plan [Member] | Current Liability [Member]
Defined Benefit Plan Disclosure [Line Items]
Current liability	(2)		(2)
Defined Benefit Plan Change In Benefit Obligation [Member] | Pension Plan [Member] | Long-term Liability [Member]
Defined Benefit Plan Disclosure [Line Items]
Long-term liability	(287)		(168)
Net liability at December 31,	(192)		(53)
Defined Benefit Plan Change In Benefit Obligation [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation, December 31,	1,098		960
Funded status at end of year	(192)		(53)
Benefits paid	(70)		(65)
Benefit obligation, January 1,	960		1,046
Service cost	24		29
Interest cost	47		43
Actuarial loss (gain)	137		(93)
Defined Benefit Plan Change In Benefit Obligation [Member] | Other Postretirement Benefit Plan [Member] | Long-term Asset [Member]
Defined Benefit Plan Disclosure [Line Items]
Long-term asset (2)		[1]		[1]
Defined Benefit Plan Change In Benefit Obligation [Member] | Other Postretirement Benefit Plan [Member] | Long-term Liability [Member]
Defined Benefit Plan Disclosure [Line Items]
Long-term liability	(235)		(233)
Net liability at December 31,	(235)		(233)
Defined Benefit Plan Change In Benefit Obligation [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Employee contributions	1		3
Benefit obligation, December 31,	334		326
Funded status at end of year	(235)		(233)
Benefits paid	(19)		(23)
Benefit obligation, January 1,	326		354
Service cost	2		3
Interest cost	15		14
Actuarial loss (gain)	8		(26)
Medicare Part D reimbursements	1		1
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, January 1,	916	[2]
Service cost	24		29		28
Interest cost	47		43		44
Fair value of plan assets, December 31,	914	[2]	916	[2]
Accumulated benefit obligation (1)	1,027	[3]	902	[3]
Discount rate	4.20%		5.00%
Rate of compensation increase	3.70%		3.70%
Pension band increase (3)	2.00%	[4]	2.00%	[4]
Other Postretirement Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, January 1,	84
Service cost	2		3		4
Interest cost	15		14		16
Fair value of plan assets, December 31,	90		84
Accumulated benefit obligation (1)		[3]		[3]
Discount rate	4.00%		4.70%
Rate of compensation increase	3.70%		3.70%
Pension band increase (3)		[4]		[4]

[1] As a result of historically having multiple plans, a portion of our obligation is in an asset position.

[2] Includes $9 million at December 31, 2014 and December 31, 2013 of medical benefit (health and welfare) component for 401h accounts to fund a portion of the other retirement benefits.

[3] APBO differs from the projected benefit obligation in that APBO excludes the effect of salary and wage increases.

[4] Only applicable to the Nicor Gas union employees.