Consolidated Statements Of Income - USD ($) shares in Millions, $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Revenue	$ 3,712	$ 3,685	$ 14,950	$ 14,024	$ 13,211
Expense:
Compensation and benefits			8,605	8,085	7,694
Other operating expenses			3,584	3,284	3,086
Operating expenses			12,189	11,369	10,780
Operating income	621	670	2,761	2,655	2,431
Other net benefits credits			215	201	233
Interest income			11	9	5
Interest expense			(290)	(237)	(189)
Investment (loss) income			(12)	15
Acquisition related derivative contracts			(441)	0	0
Income before income taxes			2,244	2,643	2,480
Income tax expense			574	1,133	685
Income from continuing operations	159	28	1,670	1,510	1,795
Discontinued operations, net of tax		2	0	2	0
Net income before non-controlling interests			1,670	1,512	1,795
Less: Net income attributable to non-controlling interests			20	20	27
Net income attributable to the Company	$ 153	$ 29	$ 1,650	$ 1,492	$ 1,768
Basic Per Share Data:
Basic net income per share – Continuing operations (in dollars per share)	$ 0.30	$ 0.05	$ 3.26	$ 2.91	$ 3.41
Net income attributable to the Company (in dollars per share)	0.30	0.06	3.26	2.91	3.41
Diluted Per Share Data:
Diluted net income per share - Continuing operations (in dollars per share)	0.30	0.05	3.23	2.87	3.38
Net income attributable to the Company (in dollars per share)	$ 0.30	$ 0.06	$ 3.23	$ 2.87	$ 3.38
Average number of shares outstanding
Basic (in shares)			506	513	519
Diluted (in shares)			511	519	524
Shares outstanding at December 31 (in shares)	504	509	504	509	514