How do I reference an Apostolic letter (Papal document) like Mulieris Dignitatem in Chicago notes style?

Papal Documents accessed online

Footnotes:

1. John Paul II, Apostolic letter on the Dignity and Vocation of Women Mulieris dignitatem (15 August 1988), 5, at The Holy See,  http://w2.vatican.va/content/john-paul-ii/en/apost_letters/1988/documents/hf_jp-ii_apl_19880815_mulieris-dignitatem.html (hereafter cited as MD).

2. MD, 7.

Bibliography:

John Paul II. Apostolic letter on the Dignity and Vocation of Women Mulieris dignitatem (15 August 1988), at The Holy See, http://w2.vatican.va/content/john-paul-ii/en/apost_letters/1988/documents/hf_jp-ii_apl_19880815_mulieris-dignitatem.html.