Benefit Obligations (Pension and Other Postretirement Obligations Narrative) (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Mar. 27, 2014	Nov. 05, 2013
Defined Benefit Plan Disclosure [Line Items]
Multiemployer plans, funded status			At least 80 percent	At least 80 percent	At least 80 percent
Multiemployer plans, period contributions, significance of contributions			false	false
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Settlement gain (loss)			$ 0	$ 78	$ (9)
Curtailment gain (loss)			3	0	61
Amortization of prior service cost (credit)			0	0	1
Lump-sum buyout payments			0	143
Pension Benefits [Member] | UNITED KINGDOM
Defined Benefit Plan Disclosure [Line Items]
Settlement gain (loss)		$ (9)
Pension Benefits [Member] | UNITED STATES
Defined Benefit Plan Disclosure [Line Items]
Settlement gain (loss)				78
Curtailment gain (loss)		61
Lump-sum buyout payments	$ 143
Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Settlement gain (loss)			0	0	0
Curtailment gain (loss)			0	0	0
Amortization of prior service cost (credit)			0	(83)	$ (12)
Lump-sum buyout payments			$ 0	0
Postretirement Benefits [Member] | UNITED STATES
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)							$ (92)
Amortization of prior service cost (credit)		(13)		(84)
Lump-sum buyout payments		$ 23		$ 40
Narrows Union Employees [Member] | Postretirement Benefits [Member] | UNITED STATES
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)						$ (5)