Consolidated Balance Sheets (Parenthetical) $ in Millions	Mar. 31, 2018 USD ($) shares	Dec. 31, 2017 USD ($) shares
Statement of Financial Position [Abstract]
Available for sale, at amortized cost	$ 79,208	$ 77,835
Fixed maturities available for sale, hybrid financial instruments	7	5
Held to maturity, at Fair Value	14,122	14,474
Equity securities, at cost	948	737
Other investments, cost	$ 4,919	$ 4,417
Common Shares, shares issued | shares	479,783,864	479,783,864
Common Shares, shares outstanding | shares	465,831,486	463,833,179
Common Shares in treasury, shares | shares	13,952,378	15,950,685