Reportable Segments (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Operating Statistics [Line Items]
Gross Operating Revenues	$ 4,083	$ 4,053	$ 11,948	$ 11,487
Intercompany Operating Revenues	(622)	(531)	(1,733)	(1,515)
Net Operating Revenues	3,461	3,522	10,215	9,972
Income from Operations	500	543	1,367	1,476
Eastern [Member]
Operating Statistics [Line Items]
Gross Operating Revenues	778	822	2,294	2,326
Intercompany Operating Revenues	(158)	(139)	(434)	(387)
Net Operating Revenues	620	683	1,860	1,939
Income from Operations	142	146	416	407
Midwest [Member]
Operating Statistics [Line Items]
Gross Operating Revenues	833	847	2,412	2,403
Intercompany Operating Revenues	(141)	(123)	(388)	(355)
Net Operating Revenues	692	724	2,024	2,048
Income from Operations	175	175	504	460
Southern [Member]
Operating Statistics [Line Items]
Gross Operating Revenues	862	853	2,575	2,553
Intercompany Operating Revenues	(140)	(104)	(386)	(307)
Net Operating Revenues	722	749	2,189	2,246
Income from Operations	180	194	567	579
Western [Member]
Operating Statistics [Line Items]
Gross Operating Revenues	840	841	2,472	2,456
Intercompany Operating Revenues	(127)	(114)	(365)	(336)
Net Operating Revenues	713	727	2,107	2,120
Income from Operations	129	154	405	436
Wheelabrator [Member]
Operating Statistics [Line Items]
Gross Operating Revenues	218	228	631	664
Intercompany Operating Revenues	(30)	(28)	(92)	(89)
Net Operating Revenues	188	200	539	575
Income from Operations	43	57	62	112
Other [Member]
Operating Statistics [Line Items]
Gross Operating Revenues	552	462	1,564	1,085
Intercompany Operating Revenues	(26)	(23)	(68)	(41)
Net Operating Revenues	526	439	1,496	1,044
Income from Operations	(22)	(40)	(94)	(75)
Operating Group Total [Member]
Operating Statistics [Line Items]
Gross Operating Revenues	4,083	4,053	11,948	11,487
Intercompany Operating Revenues	(622)	(531)	(1,733)	(1,515)
Net Operating Revenues	3,461	3,522	10,215	9,972
Income from Operations	647	686	1,860	1,919
Corporate and Other [Member]
Operating Statistics [Line Items]
Income from Operations	$ (147)	$ (143)	$ (493)	$ (443)