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, 2018		Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Guaranteed Minimum Income Benefit
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance - Beginning of year, liabilities	$ 204		$ 559		$ 609
Balance - End of year, liabilities			204		559
Guaranteed Benefit Liability, Net	861		550		853		$ 888
Level 3 | Guaranteed Minimum Income Benefit
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance - Beginning of year, liabilities	204	[1]	559	[2]	609
Transfers Into Level 3, liabilities	0		9		0
Transfers out of Level 3, liabilities					0
Change in Net Unrealized Gains (Losses) included in OCI, Liabilities	0		0
Net Realized Gains/Losses, Liabilities	248		(364)		(50)
Purchased, liabilities	0		0		0
Sales, liabilities	0		0		0
Settlements, liabilities	0		0		0
Balance - End of year, liabilities	452	[3]	204	[1]	559	[2]
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Liabilities	248		(364)		(50)
Level 3 | Other derivative instruments
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance - Beginning of year, liabilities	2		13		6
Transfers Into Level 3, liabilities	0		0		0
Transfers out of Level 3, liabilities			(9)
Change in Net Unrealized Gains (Losses) included in OCI, Liabilities	0		0		0
Net Realized Gains/Losses, Liabilities	(2)		(2)		5
Purchased, liabilities	0		0		2
Sales, liabilities	0		0		0
Settlements, liabilities	0		0		0
Balance - End of year, liabilities	0		2		13
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Liabilities	$ 0		$ (2)		$ 5

[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 $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.

[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 $853 million at December 31, 2016 and $888 million at December 31, 2015, which includes a fair value derivative adjustment of $559 million and $609 million, respectively.

[3] 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. Refer to Note 4 c) for additional information.