Consolidated Statements Of Income - USD ($) shares in Millions, $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Revenue	$ 3,685	$ 3,364	$ 14,024	$ 13,211	$ 12,893
Expense:
Compensation and benefits			7,884	7,461	7,334
Other operating expenses			3,284	3,086	3,140
Operating expenses			11,168	10,547	10,474
Operating income	686	633	2,856	2,664	2,419
Interest income			9	5	13
Interest expense			(237)	(189)	(163)
Investment income			15	1	38
Income before income taxes			2,643	2,480	2,307
Income tax expense			1,133	685	671
Income from continuing operations	28	441	1,510	1,795	1,636
Discontinued operations, net of tax	2	0	2	0	0
Net income before non-controlling interests			1,512	1,795	1,636
Less: Net income attributable to non-controlling interests			20	27	37
Net income attributable to the Company	$ 29	$ 436	$ 1,492	$ 1,768	$ 1,599
Basic Per Share Data:
Basic net income per share – Continuing operations (in dollars per share)	$ 0.05	$ 0.85	$ 2.91	$ 3.41	$ 3.01
Net income attributable to the Company (in dollars per share)	0.06	0.85	2.91	3.41	3.01
Diluted Per Share Data:
Diluted net income per share - Continuing operations (in dollars per share)	0.05	0.84	2.87	3.38	2.98
Net income attributable to the Company (in dollars per share)	$ 0.06	$ 0.84	$ 2.87	$ 3.38	$ 2.98
Average number of shares outstanding
Basic (in shares)			513	519	531
Diluted (in shares)			519	524	536
Shares outstanding at December 31 (in shares)	509	514	509	514	522