Recent Accounting Pronouncements and Developments (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2018	Jun. 30, 2020	Jan. 01, 2020	Sep. 30, 2019	Jun. 30, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member	us-gaap:AccountingStandardsUpdate201613Member	us-gaap:AccountingStandardsUpdate201708Member
Impact of restatement on opening retained earnings, after tax	$ 7,668	$ 7,353	$ 7,578	$ 7,575		$ 7,509	$ 7,599
Retained earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Impact of restatement on opening retained earnings, after tax	$ 4,090	4,009	3,456	$ 3,979		$ 3,892	$ 3,737
Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Impact of restatement on opening retained earnings, after tax		20	(3)
Cumulative Effect, Period of Adoption, Adjustment | Retained earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Impact of restatement on opening retained earnings, after tax		$ 20	$ (3)
Cumulative Effect, Period of Adoption, Adjustment | Retained earnings | ASU 2016-13
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Impact of restatement on opening retained earnings, after tax					$ 20