Benefit Plans (Summary of the components of net periodic benefit cost recognized for pension plans) (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 [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 28	$ 23	$ 86	$ 76
Interest cost	25	23	74	69
Estimated return on plan assets	(51)	(49)	(149)	(147)
Amortization and other	18	9	52	22
Net periodic benefit cost	20	6	63	20
Nonqualified [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	2	2	6	5
Interest cost	2	2	7	7
Estimated return on plan assets	0	0	0	0
Amortization and other	2	1	4	3
Net periodic benefit cost	$ 6	$ 5	$ 17	$ 15