Restructuring And Transaction Costs (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Restructuring Cost And Reserve [Line Items]
Restructuring and transaction costs	$ 267	$ 78	$ 46
Reduction of workforce [Member]
Restructuring Cost And Reserve [Line Items]
Expense associated with accelerated awards	60
Canadian Divestitures [Member]
Restructuring Cost And Reserve [Line Items]
Expense associated with accelerated awards			15
Estimated Defined Benefit Settlements [Member] | Reduction of workforce [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and transaction costs	24
Employee Related Costs [Member] | Reduction of workforce [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and transaction costs	227	24
Employee Related Costs [Member] | Canadian Divestitures [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and transaction costs			$ 46
Lease Obligations [Member] | Reduction of workforce [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and transaction costs	$ 20
Lease Obligations [Member] | Office Consolidation [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring and transaction costs		$ 54