Leasing Activities (Narrative) (Details) (USD $)	3 Months Ended	12 Months Ended
	Jun. 30, 2011	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Leasing Activities [Abstract]
Lease investments		$ 1,300,000,000	$ 1,400,000,000
Pre-tax charge due to tax law change		7,000,000
After-tax charge due to tax law change		3,000,000
Aggregate cash proceeds		161,000,000
Reduction in energy lease investment revenue			2,000,000	3,000,000
Pre-tax gain	39,000,000	39,000,000
Lessees termination payments		423,000,000
Reversal of permanent tax benefits		22,000,000
After-tax gain	3,000,000	3,000,000
Income tax provision at statutory federal rate		14,000,000
Present value of future minimum lease payments		152,000,000
Semi-annual payments		8,000,000
Description of lease term		over a 25-year period that began in December 1994
Guaranteed residual value due at end of lease term		1
Rental expense for operating leases		46,000,000	45,000,000	45,000,000
Future minimum operating lease payments, 2012		39,000,000
Future minimum operating lease payments, 2013		36,000,000
Future minimum operating lease payments, 2014		35,000,000
Future minimum operating lease payments, 2015		32,000,000
Future minimum operating lease payments, 2016		29,000,000
Future minimum operating lease payments, thereafter		359,000,000
Minimum lease payment receivable, 2012		0
Minimum lease payment receivable, 2013		0
Minimum lease payment receivable, 2014		0
Minimum lease payment receivable, 2015		0
Minimum lease payment receivable, 2016		0
Minimum lease payment receivable, thereafter		1,349,000,000
Approximate annual commitments, 2012		15,000,000
Approximate annual commitments, 2013		15,000,000
Approximate annual commitments, 2014		15,000,000
Approximate annual commitments, 2015		15,000,000
Approximate annual commitments, 2016		15,000,000
Approximate annual commitments, thereafter		$ 46,000,000