Pension and Other Postretirement Benefit Plans (Change in Benefit Obligation) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2017	Jun. 30, 2011	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Postretirement Benefits
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation, beginning of year			$ 376	$ 441
Service cost			7	7	$ 2
Interest cost			16	18	19
Plan participants' contributions			0	6
Actuarial loss (gain)			15	(16)
Benefits paid			(40)	(54)
Plan amendments		$ (138)	16	(30)
Transfer of liabilities			0	0
Special termination benefit			4	0	0
Settlements / curtailment (gain)			0	0
Foreign currency exchange rates			0	4
Benefit obligation, end of year	$ 394		394	376	441
United States Pension Benefits | Pension Benefits
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation, beginning of year			3,415	3,470
Service cost			2	3	3
Interest cost			134	147	150
Plan participants' contributions			0	0
Actuarial loss (gain)			188	92
Benefits paid			(260)	(286)
Plan amendments			0	0
Transfer of liabilities	64		(64)	0
Special termination benefit			0	0	0
Settlements / curtailment (gain)			0	(11)
Foreign currency exchange rates			0	0
Benefit obligation, end of year	3,415		3,415	3,415	3,470
Accumulated benefit obligation, end of year	3,403		3,403	3,406
Foreign Pension Benefits | Pension Benefits
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation, beginning of year			855	865
Service cost			5	5	5
Interest cost			23	27	31
Plan participants' contributions			1	1
Actuarial loss (gain)			30	105
Benefits paid			(32)	(31)
Plan amendments			0	0
Transfer of liabilities			0	0
Special termination benefit			0	0	0
Settlements / curtailment (gain)			(12)	(16)
Foreign currency exchange rates			82	(101)
Benefit obligation, end of year	952		952	855	$ 865
Accumulated benefit obligation, end of year	$ 914		$ 914	$ 816