Reserves for Insurance Losses and Loss Adjustment Expenses (Short-duration Insurance Contracts, Claims Development) (Details) $ in Millions	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	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]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	$ 3,013
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	2,984
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented	8
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net	37	$ 32	$ 35
Short-duration Insurance Contracts, Accident Year 2012
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	421	421	422	$ 422	$ 423	$ 423	$ 423	$ 430	$ 435
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount	$ 0
Short-duration Insurance Contract, Cumulative Number of Reported Claims	772,554
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 421	421	421	421	419	418	416	412	$ 391
Short-duration Insurance Contracts, Accident Year 2013
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	368	368	368	369	370	370	365	376
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount	$ 0
Short-duration Insurance Contract, Cumulative Number of Reported Claims	672,279
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 368	368	368	368	368	366	364	$ 347
Short-duration Insurance Contracts, Accident Year 2014
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	388	388	388	388	388	389	390
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount	$ 0
Short-duration Insurance Contract, Cumulative Number of Reported Claims	525,298
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 388	388	388	388	388	388	$ 369
Short-duration Insurance Contracts, Accident Year 2015
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	272	272	272	272	271	274
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount	$ 0
Short-duration Insurance Contract, Cumulative Number of Reported Claims	342,275
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 272	272	272	272	272	$ 252
Short-duration Insurance Contracts, Accident Year 2016
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	328	328	328	327	326
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount	$ 0
Short-duration Insurance Contract, Cumulative Number of Reported Claims	476,050
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 328	328	328	327	$ 302
Short-duration Insurance Contracts, Accident Year 2017
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	315	315	314	310
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount	$ 0
Short-duration Insurance Contract, Cumulative Number of Reported Claims	481,716
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 315	315	315	$ 289
Short-duration Insurance Contracts, Accident Year 2018
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	272	272	271
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount	$ 0
Short-duration Insurance Contract, Cumulative Number of Reported Claims	506,325
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 273	273	$ 245
Short-Duration Insurance Contract, Accident Year 2019
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	306	303
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount	$ 0
Short-duration Insurance Contract, Cumulative Number of Reported Claims	541,221
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 306	$ 278
Short-Duration Insurance Contract, Accident Year 2020
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	343
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount	$ 26
Short-duration Insurance Contract, Cumulative Number of Reported Claims	472,184
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 313