Basis of Presentation and Accounting Policies (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Accumulated other comprehensive income (loss), net of tax [Member]
New Accounting Pronouncements
Cumulative effect adjustment increasing (decreasing) equity		$ (22)	$ (22)
Reclassification of certain tax effects from adoption of updated accounting guidance	$ (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), net of tax [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]
New Accounting Pronouncements
Reclassification of certain tax effects from adoption of updated accounting guidance	$ 24