Employee Retirement Plans (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Pension
Components of net pension and postretirement benefits costs
Service cost of benefits earned	$ 12	$ 9	$ 25	$ 18
Interest cost on projected benefit obligation	17	17	34	33
Expected return on plan assets	(21)	(20)	(42)	(40)
Net amortization	10	6	19	12
Net pension cost	18	12	36	23
Postretirement
Components of net pension and postretirement benefits costs
Service cost of benefits earned	0	0	1	1
Interest cost on projected benefit obligation	2	2	3	4
Net amortization	(8)	(9)	(16)	(18)
Net pension cost	$ (6)	$ (7)	$ (12)	$ (13)