Stock-Based Compensation, Dividend Restrictions, And Calculations Of Earnings Per Share Of Common Stock (Calculations Of Earnings Per Share Of Common Stock) (Detail) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended										12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012		Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011		Mar. 31, 2011	Dec. 31, 2012		Dec. 31, 2011	Dec. 31, 2010
Net income from continuing operations						$ 23	$ 80	$ 95	[1]	$ 62	$ 285		$ 260	$ 139
Net loss from discontinued operations						(4)		(1)		2	0		(3)	(107)
Net income	$ 43	$ 112	[2]	$ 62	$ 68	$ 19	$ 80	$ 94		$ 64	$ 285		$ 257	$ 32
Average shares outstanding											229,000,000		226,000,000	224,000,000
Adjustment to shares outstanding
Weighted Average Shares Outstanding for Computation of Basic Earnings Per Share of Common Stock											229,000,000		226,000,000	224,000,000
Net effect of potentially dilutive shares											1,000,000	[3]
Weighted Average Shares Outstanding for Computation of Diluted Earnings Per Share of Common Stock											230,000,000		226,000,000	224,000,000
Basic earnings per share of common stock from Continuing Operations											$ 1.25		$ 1.15	$ 0.62
Basic loss per share of common stock from discontinued operations													$ (0.01)	$ (0.48)
Basic earnings per share	$ 0.18	$ 0.49		$ 0.27	$ 0.30						$ 1.25		$ 1.14	$ 0.14
Diluted earnings per share of common stock from Continuing Operations											$ 1.24		$ 1.15	$ 0.62
Diluted loss per share of common stock from Discontinued Operations													$ (0.01)	$ (0.48)
Diluted earnings per share	$ 0.18	$ 0.49		$ 0.27	$ 0.30						$ 1.24		$ 1.14	$ 0.14
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount											0		14,900	280,266

[1] Includes $39 million pre-tax ($3 million after-tax) gain from the early termination of cross-border energy leases.

[2] Includes $39 million pre-tax ($9 million after-tax) gain from the early termination of cross-border energy leases.

[3] The number of options to purchase shares of common stock that were excluded from the calculation of diluted earnings per share as they are considered to be anti-dilutive were zero, 14,900 and 280,266 for the years ended December 31, 2012, 2011 and 2010, respectively.