Investments (Securities Pledged as Collateral Related to Repurchase Reverse Repurchase Program) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Including Not Subject to Master Netting Arrangement and Assets other than Securities Transferred	$ 104	$ 103
Financial Assets Sold under Agreements to Repurchase, Gross Including Not Subject to Master Netting Arrangement	384	554
Securities Sold under Agreements to Repurchase, Gross Including Not Subject to Master Netting Arrangement	478	671
Secured Borrowings, Gross, Difference, Amount	10	14
Obligation to Return Securities Received as Collateral	488	657
Maturity Overnight [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Including Not Subject to Master Netting Arrangement and Assets other than Securities Transferred	0	0
Financial Assets Sold under Agreements to Repurchase, Gross Including Not Subject to Master Netting Arrangement	0	0
Obligation to Return Securities Received as Collateral	0	0
Maturity Less than 30 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Including Not Subject to Master Netting Arrangement and Assets other than Securities Transferred	0	0
Financial Assets Sold under Agreements to Repurchase, Gross Including Not Subject to Master Netting Arrangement	0	0
Obligation to Return Securities Received as Collateral	0	0
Maturity 30 to 90 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Including Not Subject to Master Netting Arrangement and Assets other than Securities Transferred	0	0
Financial Assets Sold under Agreements to Repurchase, Gross Including Not Subject to Master Netting Arrangement	0	0
Obligation to Return Securities Received as Collateral	0	0
Maturity Greater than 90 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Including Not Subject to Master Netting Arrangement and Assets other than Securities Transferred	104	103
Financial Assets Sold under Agreements to Repurchase, Gross Including Not Subject to Master Netting Arrangement	384	554
Obligation to Return Securities Received as Collateral	488	657
Corporate Debt Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Including Not Subject to Master Netting Arrangement and Assets other than Securities Transferred	104	103
Financial Assets Sold under Agreements to Repurchase, Gross Including Not Subject to Master Netting Arrangement	286	254
Corporate Debt Securities [Member] | Maturity Overnight [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Including Not Subject to Master Netting Arrangement and Assets other than Securities Transferred	0	0
Financial Assets Sold under Agreements to Repurchase, Gross Including Not Subject to Master Netting Arrangement	0	0
Corporate Debt Securities [Member] | Maturity Less than 30 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Including Not Subject to Master Netting Arrangement and Assets other than Securities Transferred	0	0
Financial Assets Sold under Agreements to Repurchase, Gross Including Not Subject to Master Netting Arrangement	0	0
Corporate Debt Securities [Member] | Maturity 30 to 90 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Including Not Subject to Master Netting Arrangement and Assets other than Securities Transferred	0	0
Financial Assets Sold under Agreements to Repurchase, Gross Including Not Subject to Master Netting Arrangement	0	0
Corporate Debt Securities [Member] | Maturity Greater than 90 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Including Not Subject to Master Netting Arrangement and Assets other than Securities Transferred	104	103
Financial Assets Sold under Agreements to Repurchase, Gross Including Not Subject to Master Netting Arrangement	286	254
US Government Agencies Debt Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Financial Assets Sold under Agreements to Repurchase, Gross Including Not Subject to Master Netting Arrangement	0	221
US Government Agencies Debt Securities [Member] | Maturity Overnight [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Financial Assets Sold under Agreements to Repurchase, Gross Including Not Subject to Master Netting Arrangement	0	0
US Government Agencies Debt Securities [Member] | Maturity Less than 30 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Financial Assets Sold under Agreements to Repurchase, Gross Including Not Subject to Master Netting Arrangement	0	0
US Government Agencies Debt Securities [Member] | Maturity 30 to 90 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Financial Assets Sold under Agreements to Repurchase, Gross Including Not Subject to Master Netting Arrangement	0	0
US Government Agencies Debt Securities [Member] | Maturity Greater than 90 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Financial Assets Sold under Agreements to Repurchase, Gross Including Not Subject to Master Netting Arrangement	0	221
Debt Security, Government, Non-US [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Financial Assets Sold under Agreements to Repurchase, Gross Including Not Subject to Master Netting Arrangement	98	79
Debt Security, Government, Non-US [Member] | Maturity Overnight [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Financial Assets Sold under Agreements to Repurchase, Gross Including Not Subject to Master Netting Arrangement	0	0
Debt Security, Government, Non-US [Member] | Maturity Less than 30 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Financial Assets Sold under Agreements to Repurchase, Gross Including Not Subject to Master Netting Arrangement	0	0
Debt Security, Government, Non-US [Member] | Maturity 30 to 90 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Financial Assets Sold under Agreements to Repurchase, Gross Including Not Subject to Master Netting Arrangement	0	0
Debt Security, Government, Non-US [Member] | Maturity Greater than 90 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Financial Assets Sold under Agreements to Repurchase, Gross Including Not Subject to Master Netting Arrangement	$ 98	$ 79