Consolidated Statements of Comprehensive Income (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Net income	$ 286	$ 186	$ 250
Retirement benefit plans
Actuarial loss arising during the period (net of income tax of $16, $47 and $22)	(17)	(71)	(32)
Prior service costs arising during the period (net of income tax of $1)	1	0	0
Reclassification of losses to net benefit cost (net of income tax of $9, $7 and $5)	13	9	7
Reclassification of prior service costs to net benefit cost (net of income tax of $2, $3 and $3)	(2)	(3)	(3)
Retirement benefit plans	(5)	(65)	(28)
Cash flow hedges, net of tax
Net derivative instrument gains (losses) arising during the period (net of income tax of $0, $3 and $7)	1	(6)	(15)
Reclassification of realized derivative losses to net income (net of income tax of $3, $2 and $6)	3	4	11
Cash flow hedges, net	4	(2)	(4)
Other comprehensive loss, net of tax	(1)	(67)	(32)
Comprehensive income	285	119	218
Less comprehensive income attributable to noncontrolling interest	15	14	17
Comprehensive income attributable to AGL Resources Inc.	$ 270	$ 105	$ 201