Summary of Significant Accounting Policies Summary of Significant Accounting Policies (Intangible Assets) (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Acquired Finite-Lived Intangible Assets [Line Items]
Accumulated Amortization Of Values Of Business Acquired Distribution Agreements And Customer Relationships	$ 88	$ 80
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months	8
Finite-Lived Intangible Assets, Amortization Expense, Year Two	7
Finite-Lived Intangible Assets, Amortization Expense, Year Three	6
Finite-Lived Intangible Assets, Amortization Expense, Year Four	6
Finite-Lived Intangible Assets, Amortization Expense, Year Five	$ 6
Other Intangible Assets [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	10 years
Finite-lived Intangible Assets Acquired	$ 34	37
Accumulated Amortization Of Values Of Business Acquired Distribution Agreements And Customer Relationships	8	4
Amortization of Intangible Assets	4	$ 4	$ 1
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months	4
Finite-Lived Intangible Assets, Amortization Expense, Year Two	4
Finite-Lived Intangible Assets, Amortization Expense, Year Three	4
Finite-Lived Intangible Assets, Amortization Expense, Year Four	4
Finite-Lived Intangible Assets, Amortization Expense, Year Five	$ 4