Non-Insurance Revenues from Contracts with Customers (Performance Obligation) (Details) $ in Millions	Mar. 31, 2020 USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-04-01
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Remaining performance obligation, amount	$ 831
Remaining performance obligation, expected timing of satisfaction, period	9 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Remaining performance obligation, amount	$ 951
Remaining performance obligation, expected timing of satisfaction, period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Remaining performance obligation, amount	$ 735
Remaining performance obligation, expected timing of satisfaction, period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Remaining performance obligation, amount	$ 1,300
Remaining performance obligation, expected timing of satisfaction, period