Employment Benefit Plans (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended			6 Months Ended		3 Months Ended		6 Months Ended
	Mar. 31, 2013	Jun. 30, 2013 Pension Plans, Defined Benefit	Jun. 30, 2012 Pension Plans, Defined Benefit	Jun. 30, 2013 Pension Plans, Defined Benefit	Jun. 30, 2012 Pension Plans, Defined Benefit	Jun. 30, 2013 Other Postretirement Benefit Plans, Defined Benefit	Jun. 30, 2012 Other Postretirement Benefit Plans, Defined Benefit	Jun. 30, 2013 Other Postretirement Benefit Plans, Defined Benefit	Jun. 30, 2012 Other Postretirement Benefit Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Service cost		$ 11	$ 9	$ 23	$ 19	$ 1	$ 1	$ 1	$ 1
Interest cost		23	25	45	50	3	3	6	6
Expected return on plan assets		(31)	(29)	(62)	(59)
Amortization of net loss		4	2	8	5	1	0	2	1
Net cost recognized		7	7	14	15	5	4	9	8
Discretionary contribution by Company	$ 25