Fair value measurements Fair Value Measurements (Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation) (Details) - Level 3 - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020		Dec. 31, 2019	Dec. 31, 2018
Guaranteed Minimum Income Benefit
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance - Beginning of year, liabilities	$ 897		$ 861	$ 550
Transfers Into Level 3, liabilities	0		0	0
Transfers out of Level 3, liabilities	0		0	0
Change in Net Unrealized Gains (Losses) included in OCI, Liabilities	0		0	0
Net Realized Gains/Losses, Liabilities	202		4	248
Purchased, liabilities	0		0	0
Sales, liabilities	0		0	0
Settlements, liabilities	0		0	0
Balance - End of year, liabilities	1,089	[1]	897	861
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Liabilities	202		4	248
Fair Value, Liability, Recurring Basis, Still Held, Unrealized Gain (Loss), OCI	$ 0		0
Other derivative instruments
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance - Beginning of year, liabilities			$ 0	2
Transfers Into Level 3, liabilities				0
Transfers out of Level 3, liabilities				0
Change in Net Unrealized Gains (Losses) included in OCI, Liabilities				0
Net Realized Gains/Losses, Liabilities				(2)
Purchased, liabilities				0
Sales, liabilities				0
Settlements, liabilities				0
Balance - End of year, liabilities				0
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Liabilities				$ 0

[1] Our GLB reinsurance product meets the definition of a derivative instrument for accounting purposes and is accordingly carried at fair value.