Pension and Other Postretirement Benefits - Cost of our Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Pension Benefits [Member]
Components of net pension and other postretirement benefits cost [Abstract]
Service cost	$ 2	$ 2	$ 2
Interest cost	199	194	206
Expected long-term return on plan assets	(249)	(267)	(264)
Amortization of net loss from past experience	65	70	57
Amortization of prior service cost	1	0	0
Settlement loss	0	0	6
Defined benefit plan cost	18	(1)	7
Other Postretirement Benefits [Member]
Components of net pension and other postretirement benefits cost [Abstract]
Service cost	0	0	0
Interest cost	11	11	12
Expected long-term return on plan assets	0	0	0
Amortization of net loss from past experience	1	0	0
Amortization of prior service cost	(3)	(3)	(3)
Settlement loss	0	0	0
Defined benefit plan cost	$ 9	$ 8	$ 9