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Carrying value as of the balance sheet date of short-term borrowings using unsecured obligations issued by banks, corporations and other borrowers to investors. The maturities of these money market securities generally do not exceed 270 days.

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Debt (Narrative) (Details) £ in Billions	1 Months Ended			3 Months Ended		6 Months Ended		12 Months Ended
Debt (Narrative) (Details) £ in Billions	Jun. 30, 2019 USD ($)	Apr. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)	Apr. 01, 2019 USD ($)	Mar. 31, 2019 EUR (€)	Jan. 31, 2019 USD ($)	Oct. 01, 2018 USD ($)	Sep. 30, 2018 USD ($)	Sep. 18, 2018 GBP (£)
Debt Instrument [Line Items]
Commercial paper outstanding	$ 549,000,000			$ 549,000,000		$ 549,000,000		$ 0
Payments for early extinguishment of debt						$ 585,000,000	$ 0
1.349% Senior Debt Obligations Due 2026
Debt Instrument [Line Items]
Interest rate	1.349%			1.349%		1.349%
1.979% Senior Debt Obligations Due 2030
Debt Instrument [Line Items]
Interest rate	1.979%			1.979%		1.979%
Loan Facility One
Debt Instrument [Line Items]
Debt facilities, maximum borrowing capacity			$ 300,000,000		$ 300,000,000
Loan Facility Two
Debt Instrument [Line Items]
Revolving credit facility, amount outstanding			$ 300,000,000		300,000,000
4.20% Senior Debt Obligations Due 2048
Debt Instrument [Line Items]
Proceeds from issuance of debt							$ 600,000,000
Interest rate	4.20%			4.20%		4.20%	4.20%
Commercial Paper
Debt Instrument [Line Items]
Debt financing program	$ 1,500,000,000			$ 1,500,000,000		$ 1,500,000,000
Effective interest rate	2.67%			2.67%		2.67%
Jardine Lloyd Thompson Group plc
Debt Instrument [Line Items]
Repayments of debt	$ 553,000,000	$ 450,000,000
Payments for early extinguishment of debt				$ 32,000,000
Debt assumed in acquisition	1,044,000,000			1,044,000,000		$ 1,044,000,000			$ 1,000,000,000
Jardine Lloyd Thompson Group plc \| Bridge Loan
Debt Instrument [Line Items]
Derivative, notional amount \| £														£ 5.2
Payments of debt issuance costs								35,000,000
Amortization of debt issuance costs								$ 30,000,000
Interest expense, debt					$ 5,000,000
Senior Notes
Debt Instrument [Line Items]
Proceeds from issuance of debt											$ 5,000,000,000
Senior Notes \| Senior Debt Obligations 3.50% Due 2020
Debt Instrument [Line Items]
Proceeds from issuance of debt											$ 700,000,000
Interest rate											3.50%
Senior Notes \| Senior Debt Obligations 3.875% Due 2024
Debt Instrument [Line Items]
Proceeds from issuance of debt											$ 1,000,000,000
Interest rate											3.875%
Senior Notes \| Senior Debt Obligations 4.375% Due 2029
Debt Instrument [Line Items]
Proceeds from issuance of debt	1,500,000,000			1,500,000,000		1,500,000,000					$ 1,250,000,000
Interest rate											4.375%
Senior Notes \| Senior Debt Obligations 4.75% Due 2039
Debt Instrument [Line Items]
Proceeds from issuance of debt											$ 500,000,000
Interest rate											4.75%
Senior Notes \| Senior Debt Obligations 4.90% Due 2049
Debt Instrument [Line Items]
Proceeds from issuance of debt											$ 1,250,000,000
Interest rate											4.90%
Senior Notes \| Floating Rate Senior Notes Due 2021
Debt Instrument [Line Items]
Proceeds from issuance of debt											$ 300,000,000
Senior Notes \| 1.349% Senior Debt Obligations Due 2026
Debt Instrument [Line Items]
Proceeds from issuance of debt \| €										€ 550,000,000
Interest rate			1.349%		1.349%					1.349%
Senior Notes \| 1.979% Senior Debt Obligations Due 2030
Debt Instrument [Line Items]
Proceeds from issuance of debt \| €										€ 550,000,000
Interest rate			1.979%		1.979%					1.979%
Senior Notes \| Senior Debt Obligations 4.375% Due 2019
Debt Instrument [Line Items]
Proceeds from issuance of debt			$ 250,000,000		$ 250,000,000
Senior Notes \| Jardine Lloyd Thompson Group plc
Debt Instrument [Line Items]
Proceeds from issuance of debt \| €										€ 1,100,000,000
Term Loan Facility \| Loan Facility One
Debt Instrument [Line Items]
Term of debt			1 year
Term Loan Facility \| Loan Facility Two
Debt Instrument [Line Items]
Term of debt			3 years
Term Loan Facility \| Loan Facilities Closed March 2019
Debt Instrument [Line Items]
Revolving credit facility, amount outstanding	$ 300,000,000			$ 300,000,000		$ 300,000,000
Term of debt						1 year
Debt, average borrowing rate (percentage)	3.05%			3.05%		3.05%
Revolving Credit Facility \| Amended Revolving Credit Facility March 27, 2014
Debt Instrument [Line Items]
Revolving credit facility, amount outstanding	$ 0			$ 0		$ 0
Term of debt						5 years
Debt facilities, maximum borrowing capacity												$ 1,800,000,000	$ 1,500,000,000