Accounting Policies - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Mar. 31, 2020	Jan. 01, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Significant Accounting Policies [Line Items]
Cumulative effect of accounting change	$ 6,126	$ 6,090	$ 6,126	$ 6,090	$ 5,047		$ 6,269	$ 5,665	$ 4,972
Operating lease liability	184		184				180
Operating lease right-of-use asset	$ 163		$ 163				158
Weighted average common shares adjustment related to stock-based compensation (shares)	300,000	1,300,000	0	1,200,000
Anti-dilutive potential common shares related to stock-based compensation plans (shares)	0	0	600,000	0
Maturities of short term investments			3 months
Retained Earnings
Significant Accounting Policies [Line Items]
Cumulative effect of accounting change	$ 3,685	$ 3,914	$ 3,685	$ 3,914	$ 3,616		$ 4,009	$ 3,875	$ 3,588
Cumulative effect adjustment in period of adoption | Retained Earnings | Accounting Standards Update 2016-13
Significant Accounting Policies [Line Items]
Cumulative effect of accounting change						$ 7