Retirement Benefits Plans - Change in Plan Level 3 Assets (Details) - Fair Value, Inputs, Level 3 [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning balance	$ 93	$ 66
Gains (losses) relating to assets still held at year-end	(6)	(1)
Purchases, sales, settlements - net	14	37
Transfers into or out of Level 3	0	(9)
Beginning balance	101	93
Real Estate Funds [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning balance	7	6
Gains (losses) relating to assets still held at year-end	0	1
Purchases, sales, settlements - net	(1)	0
Transfers into or out of Level 3	0	0
Beginning balance	6	7
Other Pension Plan Assets [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Beginning balance	86	60
Gains (losses) relating to assets still held at year-end	(6)	(2)
Purchases, sales, settlements - net	15	37
Transfers into or out of Level 3	0	(9)
Beginning balance	$ 95	$ 86