Consolidated Statements of Income (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Income Statement [Abstract]
Revenue	$ 3,341	$ 3,135	$ 10,339	$ 9,847
Expense:
Compensation and benefits	1,906	1,817	5,786	5,543
Other operating expenses	838	746	2,383	2,273
Operating expenses	2,744	2,563	8,169	7,816
Operating income	597	572	2,170	2,031
Interest income	2	0	6	4
Interest expense	(60)	(47)	(178)	(141)
Investment income		1	3
Investment loss	(2)			(2)
Income before income taxes	537	525	2,001	1,892
Income tax expense	140	141	519	538
Net income before non-controlling interests	397	384	1,482	1,354
Less: Net income attributable to non-controlling interests	4	5	19	22
Net income attributable to the Company	$ 393	$ 379	$ 1,463	$ 1,332
Net Income Per Share Attributable to the Company:
Basic net income per share attributable to the Company (usd per share)	$ 0.77	$ 0.73	$ 2.85	$ 2.56
Diluted net income per share attributable to the Company (usd per share)	$ 0.76	$ 0.73	$ 2.81	$ 2.54
Average number of shares outstanding:
Average number of shares outstanding - Basic	512	518	514	520
Average number of shares outstanding - Diluted	519	523	520	525
Shares outstanding at September 30,	511	516	511	516