Fair value measurements Fair Value Measurements (Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Guaranteed Minimum Income Benefit
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance - Beginning of year, liabilities	$ 452		$ 204		$ 559
Balance - End of year, liabilities			452		204
Guaranteed Benefit Liability, Net	897		861		550		$ 853
Level 3 | Guaranteed Minimum Income Benefit
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance - Beginning of year, liabilities	452	[1]	204	[2]	559
Transfers Into Level 3, liabilities	0		0		9
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	4		248		(364)
Purchased, liabilities	0		0		0
Sales, liabilities	0		0		0
Settlements, liabilities	0		0		0
Balance - End of year, liabilities	456	[3]	452	[1]	204	[2]
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Liabilities	4		248		(364)
Fair Value, Liability, Recurring Basis, Still Held, Unrealized Gain (Loss), OCI	0
Level 3 | Other derivative instruments
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance - Beginning of year, liabilities	$ 0		2		13
Transfers Into Level 3, liabilities			0		0
Transfers out of Level 3, liabilities			0		(9)
Change in Net Unrealized Gains (Losses) included in OCI, Liabilities			0		0
Net Realized Gains/Losses, Liabilities			(2)		(2)
Purchased, liabilities			0		0
Sales, liabilities			0		0
Settlements, liabilities			0		0
Balance - End of year, liabilities			0		2
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Liabilities			$ 0		$ (2)

[1] Our GLB reinsurance product meets the definition of a derivative instrument for accounting purposes and is accordingly carried at fair value. Excluded from the table above is the portion of the GLB derivative liability classified as Future policy benefits in the Consolidated balance sheets. The liability for GLB reinsurance was $861 million at December 31, 2018 and $550 million at December 31, 2017, which includes a fair value derivative adjustment of $452 million and $204 million, respectively.

[2] Our GLB reinsurance product meets the definition of a derivative instrument for accounting purposes and is accordingly carried at fair value. Excluded from the table above is the portion of the GLB derivative liability classified as Future policy benefits in the Consolidated balance sheets. The liability for GLB reinsurance was $550 million at December 31, 2017 and $853 million at December 31, 2016, which includes a fair value derivative adjustment of $204 million and $559 million, respectively. 

[3] Excluded from the table above is the portion of the GLB derivative liability classified as Future policy benefits. Refer to Note 5 c) for additional information.