Acquisitions and Dispositions (Allocation Of Acquisition Costs) (Details) $ in Millions, £ in Billions		9 Months Ended
	Sep. 20, 2018 GBP (£)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Apr. 01, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Business Acquisition [Line Items]
Cash		$ 5,859	$ 553
Estimated fair value of deferred/contingent consideration		66	108
Total consideration		5,925	661
Allocation of purchase price:
Goodwill		14,286	$ 9,435		$ 9,599	$ 9,089
Jardine Lloyd Thompson Group plc
Business Acquisition [Line Items]
Cash		5,568
Estimated fair value of deferred/contingent consideration		0
Total consideration	£ 5.2	5,568
Allocation of purchase price:
Cash and cash equivalents		353
Accounts receivable, net		714
Other current assets		143
Fixed assets, net		89
Other intangible assets		1,613
Goodwill		4,761
Right of use assets		382
Deferred tax assets		65
Other assets		493
Total assets acquired		8,613
Current liabilities		689
Fiduciary liabilities		1,275
Less- fiduciary assets		(1,275)
Long-term debt		1,044		$ 1,000
Long-term lease liability		389
Pension, post-retirement and post-employment liabilities		248
Liabilities for errors and omissions		31
Other liabilities		349
Total liabilities assumed		2,750
Non controlling interests		295
Net assets acquired		5,568
Other
Business Acquisition [Line Items]
Cash		291
Estimated fair value of deferred/contingent consideration		66
Total consideration		357
Allocation of purchase price:
Cash and cash equivalents		6
Accounts receivable, net		5
Other current assets		0
Fixed assets, net		2
Other intangible assets		143
Goodwill		201
Right of use assets		0
Deferred tax assets		0
Other assets		8
Total assets acquired		365
Current liabilities		5
Fiduciary liabilities		0
Less- fiduciary assets		0
Long-term debt		0
Long-term lease liability		0
Pension, post-retirement and post-employment liabilities		0
Liabilities for errors and omissions		0
Other liabilities		3
Total liabilities assumed		8
Non controlling interests		0
Net assets acquired		357
Current Fiscal Period Acquisitions
Business Acquisition [Line Items]
Cash		5,859
Estimated fair value of deferred/contingent consideration		66
Total consideration		5,925
Allocation of purchase price:
Cash and cash equivalents		359
Accounts receivable, net		719
Other current assets		143
Fixed assets, net		91
Other intangible assets		1,756
Goodwill		4,962
Right of use assets		382
Deferred tax assets		65
Other assets		501
Total assets acquired		8,978
Current liabilities		694
Fiduciary liabilities		1,275
Less- fiduciary assets		(1,275)
Long-term debt		1,044
Long-term lease liability		389
Pension, post-retirement and post-employment liabilities		248
Liabilities for errors and omissions		31
Other liabilities		352
Total liabilities assumed		2,758
Non controlling interests		295
Net assets acquired		$ 5,925