Summary of Significant Accounting Policies (Details) - Updated Guidance - USD ($) $ in Millions		12 Months Ended
	Jan. 01, 2018	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Member]
New Accounting Pronouncements
Cumulative effect adjustment increasing (decreasing) equity	$ (22)		$ (22)
Reclassification of certain tax effects from adoption of updated accounting guidance	(24)	$ (24)
Retained earnings [Member]
New Accounting Pronouncements
Cumulative effect adjustment increasing (decreasing) equity			$ 22
Reclassification of certain tax effects from adoption of updated accounting guidance		$ 24
Accounting Standards Update 2016-01 [Member] | Accumulated Other Comprehensive Income (Loss) [Member]
New Accounting Pronouncements
Cumulative effect adjustment increasing (decreasing) equity	(22)
Accounting Standards Update 2016-01 [Member] | Retained earnings [Member]
New Accounting Pronouncements
Cumulative effect adjustment increasing (decreasing) equity	22
Accounting Standards Update 2018-02 [Member] | Accumulated Other Comprehensive Income (Loss) [Member]
New Accounting Pronouncements
Reclassification of certain tax effects from adoption of updated accounting guidance	(24)
Accounting Standards Update 2018-02 [Member] | Retained earnings [Member]
New Accounting Pronouncements
Reclassification of certain tax effects from adoption of updated accounting guidance	$ 24