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Claims, Lawsuits, and Other Contingencies - Narrative (Details) $ in Millions				3 Months Ended	6 Months Ended	12 Months Ended
	Jun. 30, 2020 USD ($)	Sep. 06, 2018 USD ($)	Oct. 03, 2017 NZD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2019 USD ($)
Legal, Guarantees and Indemnifications
Maximum potential funding under commitments	$ 89,000,000			$ 89,000,000	$ 89,000,000		$ 110,000,000
Letters of credit outstanding	73,000,000			73,000,000	73,000,000		$ 73,000,000
Discontinued Operations, Disposed of by Sale \| Property Lease Guarantee \| Tempo Business
Legal, Guarantees and Indemnifications
Maximum potential funding under commitments	62,000,000			62,000,000	62,000,000
Guarantor obligations, current carrying value	10,000,000			10,000,000	10,000,000
Loss contingency accrual payments				0	0
Discontinued Operations, Disposed of by Sale \| Performance Guarantee \| Tempo Business
Legal, Guarantees and Indemnifications
Maximum potential funding under commitments	127,000,000			127,000,000	127,000,000
Guarantor obligations, current carrying value	1,000,000			1,000,000	1,000,000
Loss contingency accrual payments				0	0
Aviation and Aerospace Broking Industry
Legal, Guarantees and Indemnifications
Revenue						$ 100,000,000
Christchurch City Council \| Pending Litigation
Legal, Guarantees and Indemnifications
Damages sought	339,000,000		$ 528
Minimum
Legal, Guarantees and Indemnifications
Estimate of possible loss	0			0	0
Minimum \| Pilkington North America, Inc.
Legal, Guarantees and Indemnifications
Damages sought		$ 45,000,000
Maximum
Legal, Guarantees and Indemnifications
Estimate of possible loss	$ 100,000,000			$ 100,000,000	$ 100,000,000
Maximum \| Pilkington North America, Inc.
Legal, Guarantees and Indemnifications
Damages sought		85,000,000
Damages awarded		$ 15,000,000