Reserves for Insurance Losses and Loss Adjustment Expenses (Short-duration Insurance Contracts, Claims Development) (Details) $ in Millions	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)
Claims Development [Line Items]
Incurred claims and allocated loss adjustment expenses, net of reinsurance	$ 2,363
Cumulative paid claims and allocated adjustment expenses, net of insurance, separately presented	2,337
All outstanding liabilities for loss and allocated loss adjustment expenses before 2012, net of reinsurance	9
Reserves for insurance losses and allocated loss adjustment expenses, net of reinsurance	35	$ 30	$ 38
Accident year 2012
Claims Development [Line Items]
Incurred claims and allocated loss adjustment expenses, net of reinsurance	422	422	423	$ 423	$ 423	$ 430	$ 435
Incurred but not reported (IBNR) claims plus expected development on reported claims	$ 0
Cumulative number of reported claims	772,549
Cumulative paid claims and allocated loss adjustment expenses, net of reinsurance	$ 421	421	419	418	416	412	$ 391
Accident year 2013
Claims Development [Line Items]
Incurred claims and allocated loss adjustment expenses, net of reinsurance	368	369	370	370	365	376
Incurred but not reported (IBNR) claims plus expected development on reported claims	$ 0
Cumulative number of reported claims	672,273
Cumulative paid claims and allocated loss adjustment expenses, net of reinsurance	$ 368	368	368	366	364	$ 347
Accident year 2014
Claims Development [Line Items]
Incurred claims and allocated loss adjustment expenses, net of reinsurance	388	388	388	389	390
Incurred but not reported (IBNR) claims plus expected development on reported claims	$ 0
Cumulative number of reported claims	525,297
Cumulative paid claims and allocated loss adjustment expenses, net of reinsurance	$ 388	388	388	388	$ 369
Accident year 2015
Claims Development [Line Items]
Incurred claims and allocated loss adjustment expenses, net of reinsurance	272	272	271	274
Incurred but not reported (IBNR) claims plus expected development on reported claims	$ 0
Cumulative number of reported claims	342,261
Cumulative paid claims and allocated loss adjustment expenses, net of reinsurance	$ 272	272	272	$ 252
Accident year 2016
Claims Development [Line Items]
Incurred claims and allocated loss adjustment expenses, net of reinsurance	328	327	326
Incurred but not reported (IBNR) claims plus expected development on reported claims	$ 0
Cumulative number of reported claims	475,973
Cumulative paid claims and allocated loss adjustment expenses, net of reinsurance	$ 328	327	$ 302
Accident year 2017
Claims Development [Line Items]
Incurred claims and allocated loss adjustment expenses, net of reinsurance	314	310
Incurred but not reported (IBNR) claims plus expected development on reported claims	$ 0
Cumulative number of reported claims	481,319
Cumulative paid claims and allocated loss adjustment expenses, net of reinsurance	$ 315	$ 289
Accident year 2018
Claims Development [Line Items]
Incurred claims and allocated loss adjustment expenses, net of reinsurance	271
Incurred but not reported (IBNR) claims plus expected development on reported claims	$ 19
Cumulative number of reported claims	482,605
Cumulative paid claims and allocated loss adjustment expenses, net of reinsurance	$ 245