Accumulated Other Comprehensive Loss - Schedule of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2018		Sep. 30, 2017	Sep. 30, 2018		Sep. 30, 2017
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Equity, beginning balance	$ 10,347		$ 10,387	$ 10,249	[1]	$ 10,183
Equity, ending balance	10,163	[1]	10,026	10,163	[1]	10,026
Reclassification from AOCI, Current Period, Tax	9		4	21		17
Foreign currency translation [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Equity, beginning balance	(506)		(647)	(365)		(650)
Other comprehensive (loss)/income before reclassifications	(44)		78	(185)		81
Amounts reclassified from accumulated other comprehensive income/(loss) (net of income tax)	0		0	0		0
Net current-period other comprehensive (loss)/income	(44)		78	(185)		81
Equity, ending balance	(550)		(569)	(550)		(569)
Gains and losses on cash flow hedges [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Equity, beginning balance	(5)		(39)	(10)		(82)
Other comprehensive (loss)/income before reclassifications	(4)		6	(15)		15
Amounts reclassified from accumulated other comprehensive income/(loss) (net of income tax)	5		11	21		45
Net current-period other comprehensive (loss)/income	1		17	6		60
Equity, ending balance	(4)		(22)	(4)		(22)
Defined pension and post-retirement benefit costs [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Equity, beginning balance	(1,094)		(1,090)	(1,138)		(1,152)
Other comprehensive (loss)/income before reclassifications	12		(5)	46		39
Amounts reclassified from accumulated other comprehensive income/(loss) (net of income tax)	9		10	19		28
Net current-period other comprehensive (loss)/income	21		5	65		67
Equity, ending balance	(1,073)		(1,085)	(1,073)		(1,085)
Total [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Equity, beginning balance	(1,605)		(1,776)	(1,513)		(1,884)
Other comprehensive (loss)/income before reclassifications	(36)		79	(154)		135
Amounts reclassified from accumulated other comprehensive income/(loss) (net of income tax)	14		21	40		73
Net current-period other comprehensive (loss)/income	(22)		100	(114)		208
Equity, ending balance	$ (1,627)		$ (1,676)	$ (1,627)		$ (1,676)

[1] Equity includes (a) Ordinary shares $0.000304635 nominal value; Authorized 1,510,003,775; Issued 129,912,918 (2018) and 132,139,581 (2017); Outstanding 129,912,918 (2018) and 132,139,581 (2017); (b) Ordinary shares, €1 nominal value; Authorized and Issued 40,000 shares in 2018 and 2017; and (c) Preference shares, $0.000115 nominal value; Authorized 1,000,000,000 and Issued none in 2018 and 2017.