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	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Goodwill acquired	$ 97	$ 15
Goodwill	9,739	9,194	$ 9,599	$ 9,089
Aggregate amortization expense	51	$ 45
Risk and Insurance Services Segment
Segment Reporting Information [Line Items]
Goodwill	6,900
Consulting Segment
Segment Reporting Information [Line Items]
Goodwill	$ 2,800