Financing arrangements (Debt Exchange) (Details) - Notes [Member] $ in Millions	3 Months Ended
	Jun. 30, 2016 USD ($)
6.375% notes due 2037 (6.375% 2037 Notes) [Member]
Debt Instrument [Line Items]
Principal Amount Exchanged	$ 348
6.90% notes due 2038 (6.90% 2038 Notes) [Member]
Debt Instrument [Line Items]
Principal Amount Exchanged	209
6.40% notes due 2039 (6.40% 2039 Notes) [Member]
Debt Instrument [Line Items]
Principal Amount Exchanged	534
5.75% notes due 2040 (5.75% 2040 Notes) [Member]
Debt Instrument [Line Items]
Principal Amount Exchanged	288
5.15% notes due 2041 (5.15% 2041 Notes) [Member]
Debt Instrument [Line Items]
Principal Amount Exchanged	1,276
5.65% notes due 2042 (5.65% 2042 Notes) [Member]
Debt Instrument [Line Items]
Principal Amount Exchanged	763
5.375% notes due 2043 (5.375% 2043 Notes) [Member]
Debt Instrument [Line Items]
Principal Amount Exchanged	$ 739