Certain Employee Benefit and Stock-Based Compensation Plans (Summary of Components of Net Periodic Benefit Cost) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Qualified Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 25	$ 24	$ 76	$ 71
Interest cost	47	49	143	147
Expected return on plan assets	(70)	(75)	(212)	(224)
Amortization of prior service cost	(2)	(2)	(6)	(6)
Amortization of actuarial losses	22	5	66	14
Net periodic cost (benefit)	22	1	67	2
Nonqualified Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	1	3	3
Interest cost	3	3	10	10
Amortization of actuarial losses	2	1	5	3
Net periodic cost (benefit)	6	5	18	16
Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	1	4	5
Interest cost	4	5	12	14
Amortization of prior service cost		(1)	(2)	(2)
Net periodic cost (benefit)	$ 5	$ 5	$ 14	$ 17