Recent Accounting Pronouncements (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative-effect decrease to beginning retained earnings	$ (33,028)	$ (34,595)	$ (33,287)	$ (2,546)	$ (2,394)	$ (2,293)
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member	us-gaap:AccountingStandardsUpdate201613Member
Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative-effect decrease to beginning retained earnings		$ 45
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative-effect decrease to beginning retained earnings	$ (12,877)	(12,528)	$ (12,875)	$ (12,083)	$ (11,860)	$ (11,635)
Retained Earnings | Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative-effect decrease to beginning retained earnings		$ 45