Claim and Claim Adjustment Expense Reserves (International - Short Duration Contracts) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total net liability for unpaid claim and claim adjustment expenses	$ 18,701	$ 17,885	$ 17,965	$ 18,070
International
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total net liability for unpaid claim and claim adjustment expenses	1,822	$ 1,628
Excluding Hardy | International
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total net liability for unpaid claim and claim adjustment expenses	1,282
Hardy | International
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total net liability for unpaid claim and claim adjustment expenses	$ 540