Selected Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Selected Quarterly Financial Information [Abstract]
Total revenues	$ 20,187.9	$ 19,901.6	$ 20,015.5	$ 19,051.5	$ 18,984.3	$ 18,557.0	$ 18,473.4	$ 17,859.4	$ 79,156.5	$ 73,874.1	$ 71,023.5
Income from continuing operations before income taxes	374.3	1,129.6	1,558.0	1,569.1	887.1	1,087.2	1,263.7	1,130.1	4,631.0	4,368.1	3,840.2
Income from continuing operations					506.7	630.9	731.1	691.4	2,560.0	2,560.1	2,634.3
Income from discontinued operations, net of tax					0.0	0.0	0.0	9.6	0.0	9.6	(144.6)
Net income	$ 180.9	$ 654.8	$ 859.1	$ 865.2	$ 506.7	$ 630.9	$ 731.1	$ 701.0	$ 2,560.0	$ 2,569.7	$ 2,489.7
Basic net income per share - continuing operations					$ 1.88	$ 2.31	$ 2.64	$ 2.43	$ 9.73	$ 9.28	$ 8.83
Basic net income per share - discontinued operations					0.00	0.00	0.00	0.03	0.00	0.03	(0.49)
Basic net income per share	$ 0.69	$ 2.51	$ 3.27	$ 3.25	1.88	2.31	2.64	2.46	9.73	9.31	8.34
Diluted net income per share - continuing operations					1.80	2.22	2.56	2.37	9.38	8.96	8.67
Diluted net income per share - discontinued operations					0.00	0.00	0.00	0.03	0.00	0.03	(0.47)
Diluted net income per share	$ 0.68	$ 2.43	$ 3.13	$ 3.09	$ 1.80	$ 2.22	$ 2.56	$ 2.40	$ 9.38	$ 8.99	$ 8.20