Consolidated Statements of Income (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
Revenue	$ 3,504	$ 3,341	$ 11,238	$ 10,339
Expense:
Compensation and benefits	2,083	1,968	6,442	5,971
Other operating expenses	880	838	2,656	2,383
Operating expenses	2,963	2,806	9,098	8,354
Operating income	541	535	2,140	1,985
Other net benefit credits	63	62	194	185
Interest income	2	2	8	6
Interest expense	(69)	(60)	(198)	(178)
Investment (loss) income	(52)	(2)	(24)	3
Change in fair value of acquisition related FX contract	(100)	0	(100)	0
Income before income taxes	385	537	2,020	2,001
Income tax expense	106	140	509	519
Net income before non-controlling interests	279	397	1,511	1,482
Less: Net income attributable to non-controlling interests	3	4	14	19
Net income attributable to the Company	$ 276	$ 393	$ 1,497	$ 1,463
Net Income Per Share Attributable to the Company:
Basic net income per share attributable to the Company (usd per share)	$ 0.55	$ 0.77	$ 2.96	$ 2.85
Diluted net income per share attributable to the Company (usd per share)	$ 0.54	$ 0.76	$ 2.93	$ 2.81
Average number of shares outstanding:
Average number of shares outstanding - Basic	504	512	506	514
Average number of shares outstanding - Diluted	510	519	512	520
Shares outstanding at September 30,	504	511	504	511