Leasing Activities (Narrative) (Detail) (USD $)	3 Months Ended			9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Jun. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Leases [Line Items]
Lease investments	$ 1,200,000,000			$ 1,200,000,000		$ 1,300,000,000
Aggregate cash proceeds	202,000,000		161,000,000
Lease termination payments	520,000,000		423,000,000
Pre-tax gain	39,000,000		39,000,000	39,000,000	39,000,000
Reversal of permanent tax benefits	16,000,000		22,000,000	16,000,000	22,000,000
After-tax gain				9,000,000	3,000,000
Income tax provision at statutory federal rate				14,000,000	14,000,000
Pretax effect of revised lease rerun		7,000,000
Aftertax effect of revised lease rerun		$ 3,000,000