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		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Qualified [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 29	$ 27	$ 58	$ 53
Interest cost	24	23	49	46
Estimated return on plan assets	(49)	(49)	(98)	(98)
Net amortization and other	17	6	34	13
Net periodic benefit cost	21	7	43	14
Nonqualified [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	2	1	4	3
Interest cost	2	3	5	5
Estimated return on plan assets	0	0	0	0
Net amortization and other	1	1	2	2
Net periodic benefit cost	$ 5	$ 5	$ 11	$ 10