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, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Qualified [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 37	$ 29	$ 74	$ 58
Interest cost	27	24	54	49
Estimated return on plan assets	(64)	(49)	(128)	(98)
Net Amortization and other	20	17	40	34
Net periodic benefit cost	20	21	40	43
Nonqualified [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	3	2	6	4
Interest cost	4	2	7	5
Estimated return on plan assets	0	0	0	0
Net Amortization and other	3	1	6	2
Net periodic benefit cost	$ 10	$ 5	$ 19	$ 11