The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

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Goodwill and Other Intangibles (Narrative) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Goodwill acquired	$ 4,962	$ 410
Goodwill	14,286	9,435	$ 9,599	$ 9,089
Aggregate amortization expense	235	$ 135
Risk and Insurance Services Segment
Segment Reporting Information [Line Items]
Goodwill acquired	201
Goodwill	11,300
Consulting Segment
Segment Reporting Information [Line Items]
Goodwill	3,000
Jardine Lloyd Thompson Group plc
Segment Reporting Information [Line Items]
Goodwill acquired	4,800
Goodwill	$ 4,761