Employee Benefits - Estimated Future Benefit Payments (Details) - Pension Plan $ in Millions	Dec. 31, 2017 USD ($)
U.K.
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
2018	$ 134
2019	141
2020	145
2021	151
2022	159
2023 - 2027	858
U.S.
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
2018	170
2019	176
2020	182
2021	187
2022	182
2023 - 2027	901
Other
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
2018	43
2019	45
2020	46
2021	47
2022	48
2023 - 2027	$ 257

Amount of benefits for defined benefit plan expected to be paid in five fiscal years after fifth fiscal year following latest fiscal year.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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Amount of benefits for defined benefit plan expected to be paid in next fiscal year following latest fiscal year.

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Amount of benefits for defined benefit plan expected to be paid in fourth fiscal year following latest fiscal year.

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Amount of benefits for defined benefit plan expected to be paid in third fiscal year following latest fiscal year.

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Amount of benefits for defined benefit plan expected to be paid in second fiscal year following latest fiscal year.

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