Available-For-Sale Securities (Securities Held In The Rabbi Trust) (Detail) (Rabbi Trust [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Schedule of Available-for-sale Securities [Line Items]
Proceeds from Sale and Maturity of Available-for-sale Securities	$ 233	$ 0	$ 158
Gross Realized Gains	6	0	31
Gross Realized Losses	0	0	0
Net Realized Gains (Losses)	6	0	31
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	13	16
Gross Unrealized Gains	5	3
Gross Unrealized Losses	0	0
Estimated Fair Value	18	19
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost		148
Gross Unrealized Gains		5
Gross Unrealized Losses		0
Estimated Fair Value		153
Total Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	175	164
Gross Unrealized Gains	10	8
Gross Unrealized Losses	0	0
Estimated Fair Value	185	172
Government Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	114
Gross Unrealized Gains	3
Gross Unrealized Losses	0
Estimated Fair Value	117
Other Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	45
Gross Unrealized Gains	2
Gross Unrealized Losses	0
Estimated Fair Value	47
Total Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	159
Gross Unrealized Gains	5
Gross Unrealized Losses	0
Estimated Fair Value	164
Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	3
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Estimated Fair Value	$ 3