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Summary of Significant Accounting Policies and Nature of Operations Adoption of ASU 2016-13 Measurement of Credit Losses on Financial Instruments (Details) - USD ($) $ in Millions	Mar. 31, 2020	Jan. 01, 2020
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption	$ 147
Accounting Standards Update 2016-13
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred tax asset		$ 52
Cumulative Effect of New Accounting Principle in Period of Adoption	$ 147
Accounting Standards Update 2016-13 \| Cumulative Effect, Period Of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses		$ 199