Stock-Based Compensation (Schedule of Stock-Based Compensation Expense) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Pretax stock-based compensation	$ 19	$ 11	$ 46	$ 19
Tax benefit associated with stock-based compensation	8	4	18	7
Stock-based compensation cost capitalized	1	1	2	1
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Pretax stock-based compensation			2	2
Restricted Stock Units Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Pretax stock-based compensation	12	6	26	14
Performance Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Pretax stock-based compensation	$ 7	$ 5	$ 18	$ 3