Shareholders' Equity (Details) - USD ($) shares in Thousands, $ 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	Oct. 31, 2013
Purchase for treasury									$ 749.5	$ 800.0	$ 1,600.0
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	$ 14,590.3				$ 15,388.1				$ 14,590.3	$ 15,388.1
Common stock shares in treasury, shares in thousands	796				810				796	810
Net income	$ 478.4	$ 799.7	$ 600.8	$ 529.5	$ 428.5	$ 500.6	$ 733.5	$ 727.9	$ 2,408.4	$ 2,390.5	4,684.8
Treasury Stock, Retired, Cost Method, Amount									$ 0.0	$ 0.0	0.0
Preferred Stock, Shares Authorized	5,000								5,000
Preferred Stock, Shares Issued	0				0				0	0
Common Stock, Shares Held in Employee Trust, Shares	50,000				50,000				50,000	50,000
Employee benefit trust	$ 3,013.2				$ 3,013.2				$ 3,013.2	$ 3,013.2
Other comprehensive income (loss)									(588.9)	(1,989.1)	1,794.4
Allocated Share-based Compensation Expense									$ 217.8	$ 156.0	144.9
Issued shares, shares in thousands	1,106,063				1,111,437				1,106,063	1,111,437
Retained Earnings [Member]
Net income									$ 2,408.4	$ 2,390.5	4,684.8
Treasury Stock, Retired, Cost Method, Amount									(743.3)	(792.1)	(1,677.8)
Treasury Stock [Member]
Purchase for treasury									749.5	800.0	1,600.0
Treasury Stock, Retired, Cost Method, Amount									$ (749.5)	$ (800.0)	$ (1,698.1)
Treasury Stock, Shares, Retired									(9,877)	(12,579)	(32,406)
2012 Share Repurchase Program [Member]
Purchase for treasury											$ 1,100.0
Stock Repurchase Program, Authorized Amount											1,500.0
2013 Share Repurchase Program [Member]
Purchase for treasury									$ 749.5	$ 800.0	$ 500.0
Stock Repurchase Program, Authorized Amount												$ 5,000.0
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 2,950.0								$ 2,950.0