Statement of Financial Position (Parentheticals) $ in Millions	Mar. 31, 2021 USD ($) shares	Dec. 31, 2020 USD ($) shares
Statement of Financial Position [Abstract]
Available for sale, at amortized cost	$ 87,873	$ 85,188
Debt Securities, Available-for-sale, Allowance for Credit Loss	15	20
Held to maturity, Fair Value	11,752	12,510
Debt Securities, Held-to-maturity, Allowance for Credit Loss	43	44
short-term investments amortized cost	3,736	4,349
Premium Receivable, Allowance for Credit Loss	43	44
Reinsurance Recoverable, Allowance for Credit Loss	$ 317	$ 314
Common Shares, shares issued | shares	477,605,264	477,605,264
Common Shares, shares outstanding | shares	449,676,959	450,732,625
Common Shares in treasury, shares | shares	27,928,305	26,872,639