Pension and Other Postretirement Benefits - Funded Status (Details) - United States [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension Benefits [Member]
Change in benefit obligation [Abstract]
Benefit obligation, January 1	$ 4,969	$ 4,888
Service cost	3	3	$ 2
Interest cost	169	186	199
Assumed in acquisition	137	0
Partial litigation settlement - attorneys' fees	32	0
(Gain) loss from past experience	(235)	181
Benefits paid from plan assets	(314)	(277)
Benefits paid - other	(20)	(12)
Benefit obligation, December 31	4,741	4,969	4,888
Change in plan assets [Roll Forward]
Fair value of plan assets, January 1	4,281	3,977
Assumed in acquisition	96	0
Actual return on plan assets	85	418
Benefits paid	(314)	(277)
Contributions	3	163
Fair value of plan assets, December 31	4,151	4,281	3,977
Funded Status	(590)	(688)
Current liability recorded in Accrued expenses and other liabilities	(30)	(25)
Non-current liability recorded in Other non-current assets	(560)	(663)
Pension Benefits [Member] | Qualified Plan [Member]
Change in plan assets [Roll Forward]
Expected total pension plan contributions for next fiscal year	0
Pension Benefits [Member] | Non-qualifed Plan [Member]
Change in plan assets [Roll Forward]
Fair value of plan assets, December 31	0
Other Postretirement Benefits [Member]
Change in benefit obligation [Abstract]
Benefit obligation, January 1	258	277
Service cost	0	0	0
Interest cost	8	9	11
Assumed in acquisition	0	0
Partial litigation settlement - attorneys' fees	0	0
(Gain) loss from past experience	(31)	1
Benefits paid from plan assets	0	(3)
Benefits paid - other	(25)	(26)
Benefit obligation, December 31	210	258	277
Change in plan assets [Roll Forward]
Fair value of plan assets, January 1	2	5
Assumed in acquisition	0	0
Actual return on plan assets	0	0
Benefits paid	(2)	(3)
Contributions	0	0
Fair value of plan assets, December 31	0	2	$ 5
Funded Status	(210)	(256)
Current liability recorded in Accrued expenses and other liabilities	(23)	(27)
Non-current liability recorded in Other non-current assets	(187)	$ (229)
Other Postretirement Benefits [Member] | Non-qualifed Plan [Member]
Change in plan assets [Roll Forward]
Fair value of plan assets, December 31	$ 0