Nature of Operations and Significant Accounting Policies - Recent Accounting Pronouncements (Details) - USD ($) $ in Millions	Sep. 30, 2021	Jun. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Recent Accounting Pronouncements
Stockholders' Equity	$ 16,129.2	$ 16,291.5	$ 16,617.3	$ 15,721.1	$ 15,311.0	$ 14,685.8
Retained earnings (accumulated deficit)
Recent Accounting Pronouncements
Stockholders' Equity	$ 12,583.9	$ 12,395.0	$ 11,838.0	$ 11,521.4	$ 11,441.4	11,074.3
ASU 2016-13 - CECL | Effects of implementation of accounting change
Recent Accounting Pronouncements
Stockholders' Equity						(8.4)
ASU 2016-13 - CECL | Retained earnings (accumulated deficit) | Effects of implementation of accounting change
Recent Accounting Pronouncements
Stockholders' Equity						$ (8.4)