Employee Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1	$ 1	$ 2	$ 2
Interest cost	14	14	27	28
Expected return on plan assets	(20)	(19)	(39)	(38)
Net amortization	11	7	21	15
Net periodic benefit cost	6	3	11	7
Other Postretirement Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	2	2	3
Interest cost	4	7	8	14
Expected return on plan assets	(6)	(7)	(12)	(15)
Net amortization	(1)	0	(2)	1
Net periodic benefit cost	$ (2)	$ 2	$ (4)	$ 3