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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Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Goodwill and Other Intangibles (Narrative) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Goodwill acquired	$ 374	$ 462
Goodwill, expected tax deductible amount	25	140
Goodwill	15,648	15,034	$ 15,517	$ 14,671
Aggregate amortization expense	278	$ 265
Risk and Insurance Services Segment
Segment Reporting Information [Line Items]
Goodwill	11,800
Consulting Segment
Segment Reporting Information [Line Items]
Goodwill	$ 3,800