Acquisitions and Dispositions (Allocation Of Acquisition Costs) (Details) $ in Millions, £ in Billions		6 Months Ended
	Sep. 20, 2018 GBP (£)	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Apr. 01, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Business Acquisition [Line Items]
Cash		$ 5,859	$ 160
Estimated fair value of deferred/contingent consideration		66	32
Total consideration		5,925	192
Allocation of purchase price:
Goodwill		14,479	$ 9,177		$ 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		81
Other intangible assets		1,662
Goodwill		4,695
Right of use assets		379
Deferred tax assets		57
Other assets		503
Total assets acquired		8,587
Current liabilities		699
Fiduciary liabilities		1,275
Less – cash and investments held in a fiduciary capacity		(1,275)
Long-term debt		1,044		$ 1,000
Long-term lease liabilities		386
Pension, post-retirement and post-employment liabilities		234
Liabilities for errors and omissions		31
Other liabilities		316
Total liabilities assumed		2,710
Non-controlling interests		309
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		6
Other current assets		0
Fixed assets, net		2
Other intangible assets		143
Goodwill		200
Right of use assets		0
Deferred tax assets		0
Other assets		8
Total assets acquired		365
Current liabilities		5
Fiduciary liabilities		0
Less – cash and investments held in a fiduciary capacity		0
Long-term debt		0
Long-term lease liabilities		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		720
Other current assets		143
Fixed assets, net		83
Other intangible assets		1,805
Goodwill		4,895
Right of use assets		379
Deferred tax assets		57
Other assets		511
Total assets acquired		8,952
Current liabilities		704
Fiduciary liabilities		1,275
Less – cash and investments held in a fiduciary capacity		(1,275)
Long-term debt		1,044
Long-term lease liabilities		386
Pension, post-retirement and post-employment liabilities		234
Liabilities for errors and omissions		31
Other liabilities		319
Total liabilities assumed		2,718
Non-controlling interests		309
Net assets acquired		$ 5,925