Summary of Significant Accounting Policies - Narrative (Details) $ in Millions	3 Months Ended
	Mar. 31, 2020 segment	Jan. 01, 2020 USD ($)	Dec. 31, 2019 USD ($)
Accounting Policies [Abstract]
Number of operating segments | segment	2
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Adoption of accounting standard (Note 1)			$ (643)
Allowance For Credit Losses [Member] | Cumulative Effect, Period of Adoption, Adjustment [Member] | Accounting Standards Update 2016-13 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Adoption of accounting standard (Note 1)		$ 801
Retained Earnings [Member] | Accounting Standards Update 2016-13 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Adoption of accounting standard (Note 1)		$ (643)	$ (643)