Summary of Significant Accounting Policies (Recent Accounting and Reporting Pronouncements Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2019	Jan. 01, 2018	Jan. 01, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassified premiums paid from net cash used for operating activities	$ 0	$ 0	$ 22
Reclass from net cash used in operating activities	(571)	251	134
Net cash used in financing activities	(3,533)	400	638
Net cash provided by investing activities	(3,843)	496	633
Beneficial interest obtained in securitized receivables	$ 456	1,047	1,032
Cumulative effect of change in accounting principle					$ 10	$ 60
ASU 2016-15
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassified premiums paid from net cash used for operating activities			(22)
Reclass from net cash used in operating activities		1,010	1,086
Net cash used in financing activities			(22)
Net cash provided by investing activities		$ 1,010	$ 1,086
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of change in accounting principle					6	$ 60
Retained Earnings | ASU 2017-12
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of change in accounting principle					$ (3)
Scenario, Forecast | ASU 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease, liability				$ 225